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 $32.42   7.642%   $34.8975   $34.90   $34.90   $34.90  
  Purchase #2 $240.86   12.562%   $271.1168   $271.12   $271.10   $271.10  
  Purchase #3 $82.42   6.790%   $88.0163   $88.02   $88.00   $88.00  
  Purchase #4 $228.94   4.617%   $239.5102   $239.51   $239.50   $239.50  
  Purchase #5 $14.66   11.485%   $16.3437   $16.34   $16.35   $16.30  
  Purchase #6 $158.66   13.223%   $179.6396   $179.64   $179.65   $179.60  
  Purchase #7 $148.42   11.819%   $165.9618   $165.96   $165.95   $166.00  
  7 purchase totals = $906.38       $995.4859   $995.49   $995.45   $995.40