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 $212.63   11.743%   $237.5991   $237.60   $237.60   $237.60  
  Purchase #2 $38.76   8.858%   $42.1934   $42.19   $42.20   $42.20  
  Purchase #3 $183.75   8.684%   $199.7069   $199.71   $199.70   $199.70  
  Purchase #4 $61.49   11.229%   $68.3947   $68.39   $68.40   $68.40  
  Purchase #5 $96.69   12.850%   $109.1147   $109.11   $109.10   $109.10  
  Purchase #6 $241.50   6.832%   $257.9993   $258.00   $258.00   $258.00  
  Purchase #7 $31.71   5.614%   $33.4902   $33.49   $33.50   $33.50  
  7 purchase totals = $866.53       $948.4983   $948.49   $948.50   $948.50