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 $36.33   13.611%   $41.2749   $41.27   $41.25   $41.30  
  Purchase #2 $170.73   11.225%   $189.8944   $189.89   $189.90   $189.90  
  Purchase #3 $126.67   5.651%   $133.8281   $133.83   $133.85   $133.80  
  Purchase #4 $22.65   4.408%   $23.6484   $23.65   $23.65   $23.60  
  Purchase #5 $48.73   5.122%   $51.226   $51.23   $51.25   $51.20  
  Purchase #6 $16.73   11.327%   $18.625   $18.63   $18.65   $18.60  
  Purchase #7 $194.52   4.209%   $202.7073   $202.71   $202.70   $202.70  
  7 purchase totals = $616.36       $661.2041   $661.21   $661.25   $661.10