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 $161.50   11.459%   $180.0063   $180.01   $180.00   $180.00  
  Purchase #2 $249.88   5.189%   $262.8463   $262.85   $262.85   $262.80  
  Purchase #3 $150.29   8.155%   $162.5461   $162.55   $162.55   $162.50  
  Purchase #4 $86.97   9.580%   $95.3017   $95.30   $95.30   $95.30  
  Purchase #5 $180.39   3.574%   $186.8371   $186.84   $186.85   $186.80  
  Purchase #6 $61.76   10.221%   $68.0725   $68.07   $68.05   $68.10  
  Purchase #7 $194.85   7.601%   $209.6605   $209.66   $209.65   $209.70  
  7 purchase totals = $1,085.64       $1,165.2705   $1,165.28   $1,165.25   $1,165.20