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 $204.88   10.711%   $226.8247   $226.82   $226.80   $226.80  
  Purchase #2 $209.62   8.573%   $227.5907   $227.59   $227.60   $227.60  
  Purchase #3 $6.82   6.455%   $7.2602   $7.26   $7.25   $7.30  
  Purchase #4 $111.68   13.653%   $126.9277   $126.93   $126.95   $126.90  
  Purchase #5 $118.79   11.378%   $132.3059   $132.31   $132.30   $132.30  
  Purchase #6 $65.97   6.487%   $70.2495   $70.25   $70.25   $70.20  
  Purchase #7 $7.57   5.384%   $7.9776   $7.98   $8.00   $8.00  
  7 purchase totals = $725.33       $799.1363   $799.14   $799.15   $799.10