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 $88.78   7.519%   $95.4554   $95.46   $95.45   $95.50  
  Purchase #2 $62.35   10.393%   $68.83   $68.83   $68.85   $68.80  
  Purchase #3 $235.31   11.407%   $262.1518   $262.15   $262.15   $262.20  
  Purchase #4 $35.56   7.226%   $38.1296   $38.13   $38.15   $38.10  
  Purchase #5 $197.91   5.196%   $208.1934   $208.19   $208.20   $208.20  
  Purchase #6 $70.95   10.193%   $78.1819   $78.18   $78.20   $78.20  
  Purchase #7 $152.58   13.355%   $172.9571   $172.96   $172.95   $173.00  
  7 purchase totals = $843.44       $923.8992   $923.90   $923.95   $924.00