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 $211.51   9.806%   $232.2507   $232.25   $232.25   $232.30  
  Purchase #2 $238.83   6.250%   $253.7569   $253.76   $253.75   $253.80  
  Purchase #3 $242.94   7.761%   $261.7946   $261.79   $261.80   $261.80  
  Purchase #4 $46.83   13.850%   $53.316   $53.32   $53.30   $53.30  
  Purchase #5 $108.36   8.762%   $117.8545   $117.85   $117.85   $117.90  
  Purchase #6 $169.44   4.687%   $177.3817   $177.38   $177.40   $177.40  
  Purchase #7 $143.30   11.845%   $160.2739   $160.27   $160.25   $160.30  
  7 purchase totals = $1,161.21       $1,256.6283   $1,256.62   $1,256.60   $1,256.80