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 $213.82   10.412%   $236.0829   $236.08   $236.10   $236.10  
  Purchase #2 $186.98   12.748%   $210.8162   $210.82   $210.80   $210.80  
  Purchase #3 $148.41   7.161%   $159.0376   $159.04   $159.05   $159.00  
  Purchase #4 $146.94   12.598%   $165.4515   $165.45   $165.45   $165.50  
  Purchase #5 $154.77   3.428%   $160.0755   $160.08   $160.10   $160.10  
  Purchase #6 $153.43   7.541%   $165.0002   $165.00   $165.00   $165.00  
  Purchase #7 $18.69   6.754%   $19.9523   $19.95   $19.95   $20.00  
  7 purchase totals = $1,023.04       $1,116.4162   $1,116.42   $1,116.45   $1,116.50