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 $142.34   5.216%   $149.7645   $149.76   $149.75   $149.80  
  Purchase #2 $209.32   12.267%   $234.9973   $235.00   $235.00   $235.00  
  Purchase #3 $218.89   10.837%   $242.6111   $242.61   $242.60   $242.60  
  Purchase #4 $78.47   13.357%   $88.9512   $88.95   $88.95   $89.00  
  Purchase #5 $147.46   9.271%   $161.131   $161.13   $161.15   $161.10  
  Purchase #6 $65.56   7.290%   $70.3393   $70.34   $70.35   $70.30  
  Purchase #7 $68.71   9.309%   $75.1062   $75.11   $75.10   $75.10  
  7 purchase totals = $930.75       $1,022.9006   $1,022.90   $1,022.90   $1,022.90