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 $24.88   9.574%   $27.262   $27.26   $27.25   $27.30  
  Purchase #2 $60.53   5.221%   $63.6903   $63.69   $63.70   $63.70  
  Purchase #3 $124.33   4.282%   $129.6538   $129.65   $129.65   $129.70  
  Purchase #4 $158.50   5.347%   $166.975   $166.98   $167.00   $167.00  
  Purchase #5 $230.83   11.550%   $257.4909   $257.49   $257.50   $257.50  
  Purchase #6 $186.78   6.785%   $199.453   $199.45   $199.45   $199.50  
  Purchase #7 $83.58   8.361%   $90.5681   $90.57   $90.55   $90.60  
  7 purchase totals = $869.43       $935.0931   $935.09   $935.10   $935.30