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 $111.58   11.850%   $124.8022   $124.80   $124.80   $124.80  
  Purchase #2 $66.35   10.513%   $73.3254   $73.33   $73.35   $73.30  
  Purchase #3 $148.27   7.621%   $159.5697   $159.57   $159.55   $159.60  
  Purchase #4 $78.94   12.176%   $88.5517   $88.55   $88.55   $88.60  
  Purchase #5 $26.55   11.873%   $29.7023   $29.70   $29.70   $29.70  
  Purchase #6 $135.75   9.229%   $148.2784   $148.28   $148.30   $148.30  
  Purchase #7 $88.52   12.622%   $99.693   $99.69   $99.70   $99.70  
  7 purchase totals = $655.96       $723.9227   $723.92   $723.95   $724.00