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 $219.46   5.306%   $231.1045   $231.10   $231.10   $231.10  
  Purchase #2 $146.59   9.376%   $160.3343   $160.33   $160.35   $160.30  
  Purchase #3 $88.34   5.418%   $93.1263   $93.13   $93.15   $93.10  
  Purchase #4 $226.36   10.433%   $249.9761   $249.98   $250.00   $250.00  
  Purchase #5 $98.83   4.185%   $102.966   $102.97   $102.95   $103.00  
  Purchase #6 $244.37   13.160%   $276.5291   $276.53   $276.55   $276.50  
  Purchase #7 $202.28   9.347%   $221.1871   $221.19   $221.20   $221.20  
  7 purchase totals = $1,226.23       $1,335.2234   $1,335.23   $1,335.30   $1,335.20