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 $62.68   9.261%   $68.4848   $68.48   $68.50   $68.50  
  Purchase #2 $231.55   5.183%   $243.5512   $243.55   $243.55   $243.60  
  Purchase #3 $87.88   13.588%   $99.8211   $99.82   $99.80   $99.80  
  Purchase #4 $91.41   10.811%   $101.2923   $101.29   $101.30   $101.30  
  Purchase #5 $217.93   9.258%   $238.106   $238.11   $238.10   $238.10  
  Purchase #6 $20.30   13.756%   $23.0925   $23.09   $23.10   $23.10  
  Purchase #7 $137.40   5.633%   $145.1397   $145.14   $145.15   $145.10  
  7 purchase totals = $849.15       $919.4876   $919.48   $919.50   $919.50