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 $231.85   3.621%   $240.2453   $240.25   $240.25   $240.20  
  Purchase #2 $168.68   13.617%   $191.6492   $191.65   $191.65   $191.60  
  Purchase #3 $64.60   9.344%   $70.6362   $70.64   $70.65   $70.60  
  Purchase #4 $46.33   8.697%   $50.3593   $50.36   $50.35   $50.40  
  Purchase #5 $96.34   8.136%   $104.1782   $104.18   $104.20   $104.20  
  Purchase #6 $187.70   11.479%   $209.2461   $209.25   $209.25   $209.20  
  Purchase #7 $72.37   3.325%   $74.7763   $74.78   $74.80   $74.80  
  7 purchase totals = $867.87       $941.0906   $941.11   $941.15   $941.00