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 $62.61   8.273%   $67.7897   $67.79   $67.80   $67.80  
  Purchase #2 $61.99   4.158%   $64.5675   $64.57   $64.55   $64.60  
  Purchase #3 $190.90   7.516%   $205.248   $205.25   $205.25   $205.20  
  Purchase #4 $84.41   9.597%   $92.5108   $92.51   $92.50   $92.50  
  Purchase #5 $211.78   6.238%   $224.9908   $224.99   $225.00   $225.00  
  Purchase #6 $104.74   13.549%   $118.9312   $118.93   $118.95   $118.90  
  Purchase #7 $182.27   11.812%   $203.7997   $203.80   $203.80   $203.80  
  7 purchase totals = $898.70       $977.8377   $977.84   $977.85   $977.80