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 $236.67   11.786%   $264.5639   $264.56   $264.55   $264.60  
  Purchase #2 $94.66   12.864%   $106.8371   $106.84   $106.85   $106.80  
  Purchase #3 $67.47   12.464%   $75.8795   $75.88   $75.90   $75.90  
  Purchase #4 $237.97   8.364%   $257.8738   $257.87   $257.85   $257.90  
  Purchase #5 $166.49   11.705%   $185.9777   $185.98   $186.00   $186.00  
  Purchase #6 $191.40   8.287%   $207.2613   $207.26   $207.25   $207.30  
  Purchase #7 $163.30   8.464%   $177.1217   $177.12   $177.10   $177.10  
  7 purchase totals = $1,157.96       $1,275.5150   $1,275.51   $1,275.50   $1,275.60