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 $83.96   9.430%   $91.8774   $91.88   $91.90   $91.90  
  Purchase #2 $42.98   7.231%   $46.0879   $46.09   $46.10   $46.10  
  Purchase #3 $104.26   8.179%   $112.7874   $112.79   $112.80   $112.80  
  Purchase #4 $173.66   5.226%   $182.7355   $182.74   $182.75   $182.70  
  Purchase #5 $94.39   3.827%   $98.0023   $98.00   $98.00   $98.00  
  Purchase #6 $82.77   8.352%   $89.683   $89.68   $89.70   $89.70  
  Purchase #7 $235.29   4.794%   $246.5698   $246.57   $246.55   $246.60  
  7 purchase totals = $817.31       $867.7433   $867.75   $867.80   $867.80