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 $63.45   6.352%   $67.4803   $67.48   $67.50   $67.50  
  Purchase #2 $204.31   6.191%   $216.9588   $216.96   $216.95   $217.00  
  Purchase #3 $122.52   10.622%   $135.5341   $135.53   $135.55   $135.50  
  Purchase #4 $173.92   12.656%   $195.9313   $195.93   $195.95   $195.90  
  Purchase #5 $155.76   3.329%   $160.9453   $160.95   $160.95   $160.90  
  Purchase #6 $87.28   5.843%   $92.3798   $92.38   $92.40   $92.40  
  Purchase #7 $189.92   9.185%   $207.3642   $207.36   $207.35   $207.40  
  7 purchase totals = $997.16       $1,076.5938   $1,076.59   $1,076.65   $1,076.60