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 $46.98   3.460%   $48.6055   $48.61   $48.60   $48.60  
  Purchase #2 $155.71   3.851%   $161.7064   $161.71   $161.70   $161.70  
  Purchase #3 $20.79   6.711%   $22.1852   $22.19   $22.20   $22.20  
  Purchase #4 $217.40   6.661%   $231.881   $231.88   $231.90   $231.90  
  Purchase #5 $19.34   5.240%   $20.3534   $20.35   $20.35   $20.40  
  Purchase #6 $222.25   11.579%   $247.9843   $247.98   $248.00   $248.00  
  Purchase #7 $234.55   5.554%   $247.5769   $247.58   $247.60   $247.60  
  7 purchase totals = $917.02       $980.2927   $980.30   $980.35   $980.40