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 $59.95   10.473%   $66.2286   $66.23   $66.25   $66.20  
  Purchase #2 $186.33   13.524%   $211.5293   $211.53   $211.55   $211.50  
  Purchase #3 $147.47   5.547%   $155.6502   $155.65   $155.65   $155.70  
  Purchase #4 $158.69   12.715%   $178.8674   $178.87   $178.85   $178.90  
  Purchase #5 $126.63   3.280%   $130.7835   $130.78   $130.80   $130.80  
  Purchase #6 $33.27   7.424%   $35.74   $35.74   $35.75   $35.70  
  Purchase #7 $135.93   9.595%   $148.9725   $148.97   $148.95   $149.00  
  7 purchase totals = $848.27       $927.7715   $927.77   $927.80   $927.80