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 $54.73   13.792%   $62.2784   $62.28   $62.30   $62.30  
  Purchase #2 $188.41   6.633%   $200.9072   $200.91   $200.90   $200.90  
  Purchase #3 $191.79   8.464%   $208.0231   $208.02   $208.00   $208.00  
  Purchase #4 $43.42   4.469%   $45.3604   $45.36   $45.35   $45.40  
  Purchase #5 $64.62   4.224%   $67.3495   $67.35   $67.35   $67.30  
  Purchase #6 $193.34   9.205%   $211.1369   $211.14   $211.15   $211.10  
  Purchase #7 $101.97   13.402%   $115.636   $115.64   $115.65   $115.60  
  7 purchase totals = $838.28       $910.6915   $910.70   $910.70   $910.60