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 $67.99   10.823%   $75.3486   $75.35   $75.35   $75.30  
  Purchase #2 $119.38   8.519%   $129.55   $129.55   $129.55   $129.60  
  Purchase #3 $38.98   7.499%   $41.9031   $41.90   $41.90   $41.90  
  Purchase #4 $108.95   8.641%   $118.3644   $118.36   $118.35   $118.40  
  Purchase #5 $64.62   11.443%   $72.0145   $72.01   $72.00   $72.00  
  Purchase #6 $178.38   12.417%   $200.5294   $200.53   $200.55   $200.50  
  Purchase #7 $54.50   9.130%   $59.4759   $59.48   $59.50   $59.50  
  7 purchase totals = $632.80       $697.1859   $697.18   $697.20   $697.20