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 $91.52   12.116%   $102.6086   $102.61   $102.60   $102.60  
  Purchase #2 $228.43   9.633%   $250.4347   $250.43   $250.45   $250.40  
  Purchase #3 $61.27   5.731%   $64.7814   $64.78   $64.80   $64.80  
  Purchase #4 $224.66   11.554%   $250.6172   $250.62   $250.60   $250.60  
  Purchase #5 $237.38   10.122%   $261.4076   $261.41   $261.40   $261.40  
  Purchase #6 $161.47   9.177%   $176.2881   $176.29   $176.30   $176.30  
  Purchase #7 $154.77   7.261%   $166.0078   $166.01   $166.00   $166.00  
  7 purchase totals = $1,159.50       $1,272.1454   $1,272.15   $1,272.15   $1,272.10