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 $183.91   13.599%   $208.9199   $208.92   $208.90   $208.90  
  Purchase #2 $216.42   4.764%   $226.7302   $226.73   $226.75   $226.70  
  Purchase #3 $229.79   3.561%   $237.9728   $237.97   $237.95   $238.00  
  Purchase #4 $44.63   11.495%   $49.7602   $49.76   $49.75   $49.80  
  Purchase #5 $93.37   4.288%   $97.3737   $97.37   $97.35   $97.40  
  Purchase #6 $110.94   12.703%   $125.0327   $125.03   $125.05   $125.00  
  Purchase #7 $128.28   11.201%   $142.6486   $142.65   $142.65   $142.60  
  7 purchase totals = $1,007.34       $1,088.4381   $1,088.43   $1,088.40   $1,088.40