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 $58.51   8.761%   $63.6361   $63.64   $63.65   $63.60  
  Purchase #2 $151.30   3.721%   $156.9299   $156.93   $156.95   $156.90  
  Purchase #3 $246.45   12.420%   $277.0591   $277.06   $277.05   $277.10  
  Purchase #4 $51.77   7.614%   $55.7118   $55.71   $55.70   $55.70  
  Purchase #5 $82.64   7.403%   $88.7578   $88.76   $88.75   $88.80  
  Purchase #6 $148.42   4.746%   $155.464   $155.46   $155.45   $155.50  
  Purchase #7 $96.97   8.387%   $105.1029   $105.10   $105.10   $105.10  
  7 purchase totals = $836.06       $902.6616   $902.66   $902.65   $902.70