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 $245.64   6.413%   $261.3929   $261.39   $261.40   $261.40  
  Purchase #2 $62.96   4.210%   $65.6106   $65.61   $65.60   $65.60  
  Purchase #3 $163.50   5.807%   $172.9944   $172.99   $173.00   $173.00  
  Purchase #4 $79.78   9.287%   $87.1892   $87.19   $87.20   $87.20  
  Purchase #5 $143.45   13.227%   $162.4241   $162.42   $162.40   $162.40  
  Purchase #6 $41.79   6.377%   $44.4549   $44.45   $44.45   $44.50  
  Purchase #7 $15.25   8.327%   $16.5199   $16.52   $16.50   $16.50  
  7 purchase totals = $752.37       $810.5860   $810.57   $810.55   $810.60