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 $173.45   12.655%   $195.4001   $195.40   $195.40   $195.40  
  Purchase #2 $60.48   13.859%   $68.8619   $68.86   $68.85   $68.90  
  Purchase #3 $94.71   10.852%   $104.9879   $104.99   $105.00   $105.00  
  Purchase #4 $224.36   8.436%   $243.287   $243.29   $243.30   $243.30  
  Purchase #5 $54.25   8.697%   $58.9681   $58.97   $58.95   $59.00  
  Purchase #6 $179.97   8.833%   $195.8668   $195.87   $195.85   $195.90  
  Purchase #7 $34.96   3.266%   $36.1018   $36.10   $36.10   $36.10  
  7 purchase totals = $822.18       $903.4736   $903.48   $903.45   $903.60