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 $163.32   10.803%   $180.9635   $180.96   $180.95   $181.00  
  Purchase #2 $156.44   13.867%   $178.1335   $178.13   $178.15   $178.10  
  Purchase #3 $24.25   5.124%   $25.4926   $25.49   $25.50   $25.50  
  Purchase #4 $131.47   11.635%   $146.7665   $146.77   $146.75   $146.80  
  Purchase #5 $5.95   3.548%   $6.1611   $6.16   $6.15   $6.20  
  Purchase #6 $85.60   11.706%   $95.6203   $95.62   $95.60   $95.60  
  Purchase #7 $154.79   7.517%   $166.4256   $166.43   $166.45   $166.40  
  7 purchase totals = $721.82       $799.5631   $799.56   $799.55   $799.60