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 $225.95   12.104%   $253.299   $253.30   $253.30   $253.30  
  Purchase #2 $213.41   7.647%   $229.7295   $229.73   $229.75   $229.70  
  Purchase #3 $129.58   12.695%   $146.0302   $146.03   $146.05   $146.00  
  Purchase #4 $15.68   7.760%   $16.8968   $16.90   $16.90   $16.90  
  Purchase #5 $208.93   5.561%   $220.5486   $220.55   $220.55   $220.50  
  Purchase #6 $91.62   4.836%   $96.0507   $96.05   $96.05   $96.10  
  Purchase #7 $56.34   6.437%   $59.9666   $59.97   $59.95   $60.00  
  7 purchase totals = $941.51       $1,022.5214   $1,022.53   $1,022.55   $1,022.50