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 $238.63   10.260%   $263.1134   $263.11   $263.10   $263.10  
  Purchase #2 $69.52   7.616%   $74.8146   $74.81   $74.80   $74.80  
  Purchase #3 $82.70   6.129%   $87.7687   $87.77   $87.75   $87.80  
  Purchase #4 $151.34   12.543%   $170.3226   $170.32   $170.30   $170.30  
  Purchase #5 $95.87   10.589%   $106.0217   $106.02   $106.00   $106.00  
  Purchase #6 $204.34   12.616%   $230.1195   $230.12   $230.10   $230.10  
  Purchase #7 $75.34   9.519%   $82.5116   $82.51   $82.50   $82.50  
  7 purchase totals = $917.74       $1,014.6721   $1,014.66   $1,014.55   $1,014.60