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 $112.44   12.519%   $126.5164   $126.52   $126.50   $126.50  
  Purchase #2 $104.49   8.434%   $113.3027   $113.30   $113.30   $113.30  
  Purchase #3 $154.39   9.633%   $169.2624   $169.26   $169.25   $169.30  
  Purchase #4 $234.62   7.150%   $251.3953   $251.40   $251.40   $251.40  
  Purchase #5 $120.49   5.749%   $127.417   $127.42   $127.40   $127.40  
  Purchase #6 $188.54   11.611%   $210.4314   $210.43   $210.45   $210.40  
  Purchase #7 $7.27   7.279%   $7.7992   $7.80   $7.80   $7.80  
  7 purchase totals = $922.24       $1,006.1244   $1,006.13   $1,006.10   $1,006.10