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 $87.85   8.112%   $94.9764   $94.98   $95.00   $95.00  
  Purchase #2 $112.54   4.844%   $117.9914   $117.99   $118.00   $118.00  
  Purchase #3 $24.62   6.525%   $26.2265   $26.23   $26.25   $26.20  
  Purchase #4 $111.34   7.872%   $120.1047   $120.10   $120.10   $120.10  
  Purchase #5 $66.65   10.432%   $73.6029   $73.60   $73.60   $73.60  
  Purchase #6 $172.85   12.306%   $194.1209   $194.12   $194.10   $194.10  
  Purchase #7 $9.57   3.677%   $9.9219   $9.92   $9.90   $9.90  
  7 purchase totals = $585.42       $636.9447   $636.94   $636.95   $636.90