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 $214.33   11.690%   $239.3852   $239.39   $239.40   $239.40  
  Purchase #2 $188.95   8.505%   $205.0202   $205.02   $205.00   $205.00  
  Purchase #3 $94.45   4.127%   $98.348   $98.35   $98.35   $98.30  
  Purchase #4 $37.48   10.587%   $41.448   $41.45   $41.45   $41.40  
  Purchase #5 $73.43   5.462%   $77.4407   $77.44   $77.45   $77.40  
  Purchase #6 $249.36   9.390%   $272.7749   $272.77   $272.75   $272.80  
  Purchase #7 $77.74   13.621%   $88.329   $88.33   $88.35   $88.30  
  7 purchase totals = $935.74       $1,022.7460   $1,022.75   $1,022.75   $1,022.60