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 $83.80   12.498%   $94.2733   $94.27   $94.25   $94.30  
  Purchase #2 $235.93   9.624%   $258.6359   $258.64   $258.65   $258.60  
  Purchase #3 $53.69   6.124%   $56.978   $56.98   $57.00   $57.00  
  Purchase #4 $87.96   13.198%   $99.569   $99.57   $99.55   $99.60  
  Purchase #5 $201.58   7.122%   $215.9365   $215.94   $215.95   $215.90  
  Purchase #6 $118.66   4.819%   $124.3782   $124.38   $124.40   $124.40  
  Purchase #7 $16.33   10.210%   $17.9973   $18.00   $18.00   $18.00  
  7 purchase totals = $797.95       $867.7682   $867.78   $867.80   $867.80