Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $89.26   13.556%   $101.3601   $101.36   $101.35   $101.40  
  Purchase #2 $189.41   12.778%   $213.6128   $213.61   $213.60   $213.60  
  Purchase #3 $125.55   5.115%   $131.9719   $131.97   $131.95   $132.00  
  Purchase #4 $182.53   11.785%   $204.0412   $204.04   $204.05   $204.00  
  Purchase #5 $158.30   8.563%   $171.8552   $171.86   $171.85   $171.90  
  Purchase #6 $103.53   11.379%   $115.3107   $115.31   $115.30   $115.30  
  Purchase #7 $246.89   8.190%   $267.1103   $267.11   $267.10   $267.10  
  7 purchase totals = $1,095.47       $1,205.2622   $1,205.26   $1,205.20   $1,205.30