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 $61.35   7.319%   $65.8402   $65.84   $65.85   $65.80  
  Purchase #2 $221.67   3.201%   $228.7657   $228.77   $228.75   $228.80  
  Purchase #3 $174.84   3.792%   $181.4699   $181.47   $181.45   $181.50  
  Purchase #4 $53.71   9.578%   $58.8543   $58.85   $58.85   $58.90  
  Purchase #5 $191.76   7.704%   $206.5332   $206.53   $206.55   $206.50  
  Purchase #6 $47.39   11.613%   $52.8934   $52.89   $52.90   $52.90  
  Purchase #7 $163.69   11.344%   $182.259   $182.26   $182.25   $182.30  
  7 purchase totals = $914.41       $976.6157   $976.61   $976.60   $976.70