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 $174.44   12.633%   $196.477   $196.48   $196.50   $196.50  
  Purchase #2 $189.78   7.805%   $204.5923   $204.59   $204.60   $204.60  
  Purchase #3 $235.94   3.683%   $244.6297   $244.63   $244.65   $244.60  
  Purchase #4 $231.86   7.562%   $249.3933   $249.39   $249.40   $249.40  
  Purchase #5 $31.90   13.558%   $36.225   $36.23   $36.25   $36.20  
  Purchase #6 $58.54   10.160%   $64.4877   $64.49   $64.50   $64.50  
  Purchase #7 $249.66   10.854%   $276.7581   $276.76   $276.75   $276.80  
  7 purchase totals = $1,172.12       $1,272.5631   $1,272.57   $1,272.65   $1,272.60