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 $209.37   9.700%   $229.6789   $229.68   $229.70   $229.70  
  Purchase #2 $90.63   7.391%   $97.3285   $97.33   $97.35   $97.30  
  Purchase #3 $119.97   4.748%   $125.6662   $125.67   $125.65   $125.70  
  Purchase #4 $157.48   6.598%   $167.8705   $167.87   $167.85   $167.90  
  Purchase #5 $58.91   4.401%   $61.5026   $61.50   $61.50   $61.50  
  Purchase #6 $156.93   11.741%   $175.3552   $175.36   $175.35   $175.40  
  Purchase #7 $161.93   9.515%   $177.3376   $177.34   $177.35   $177.30  
  7 purchase totals = $955.22       $1,034.7395   $1,034.75   $1,034.75   $1,034.80