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 $67.61   11.202%   $75.1837   $75.18   $75.20   $75.20  
  Purchase #2 $238.74   10.171%   $263.0222   $263.02   $263.00   $263.00  
  Purchase #3 $194.85   5.578%   $205.7187   $205.72   $205.70   $205.70  
  Purchase #4 $229.25   5.709%   $242.3379   $242.34   $242.35   $242.30  
  Purchase #5 $241.98   12.120%   $271.308   $271.31   $271.30   $271.30  
  Purchase #6 $104.76   10.115%   $115.3565   $115.36   $115.35   $115.40  
  Purchase #7 $153.33   11.131%   $170.3972   $170.40   $170.40   $170.40  
  7 purchase totals = $1,230.52       $1,343.3242   $1,343.33   $1,343.30   $1,343.30