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 $63.42   3.201%   $65.4501   $65.45   $65.45   $65.50  
  Purchase #2 $230.74   9.688%   $253.0941   $253.09   $253.10   $253.10  
  Purchase #3 $204.52   13.383%   $231.8909   $231.89   $231.90   $231.90  
  Purchase #4 $190.62   11.148%   $211.8703   $211.87   $211.85   $211.90  
  Purchase #5 $110.32   11.652%   $123.1745   $123.17   $123.15   $123.20  
  Purchase #6 $49.69   8.214%   $53.7715   $53.77   $53.75   $53.80  
  Purchase #7 $14.71   8.821%   $16.0076   $16.01   $16.00   $16.00  
  7 purchase totals = $864.02       $955.2590   $955.25   $955.20   $955.40