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 $92.56   5.293%   $97.4592   $97.46   $97.45   $97.50  
  Purchase #2 $181.76   5.817%   $192.333   $192.33   $192.35   $192.30  
  Purchase #3 $179.56   5.674%   $189.7482   $189.75   $189.75   $189.70  
  Purchase #4 $45.92   9.779%   $50.4105   $50.41   $50.40   $50.40  
  Purchase #5 $172.39   10.257%   $190.072   $190.07   $190.05   $190.10  
  Purchase #6 $46.58   9.490%   $51.0004   $51.00   $51.00   $51.00  
  Purchase #7 $30.26   13.393%   $34.3127   $34.31   $34.30   $34.30  
  7 purchase totals = $749.03       $805.3360   $805.33   $805.30   $805.30