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 $60.53   9.610%   $66.3469   $66.35   $66.35   $66.30  
  Purchase #2 $140.56   5.504%   $148.2964   $148.30   $148.30   $148.30  
  Purchase #3 $150.52   9.344%   $164.5846   $164.58   $164.60   $164.60  
  Purchase #4 $182.33   8.342%   $197.54   $197.54   $197.55   $197.50  
  Purchase #5 $80.82   5.846%   $85.5447   $85.54   $85.55   $85.50  
  Purchase #6 $68.48   9.243%   $74.8096   $74.81   $74.80   $74.80  
  Purchase #7 $44.52   10.593%   $49.236   $49.24   $49.25   $49.20  
  7 purchase totals = $727.76       $786.3582   $786.36   $786.40   $786.20