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 $61.54   9.221%   $67.2146   $67.21   $67.20   $67.20  
  Purchase #2 $209.65   8.312%   $227.0761   $227.08   $227.10   $227.10  
  Purchase #3 $194.29   8.483%   $210.7716   $210.77   $210.75   $210.80  
  Purchase #4 $94.39   4.277%   $98.4271   $98.43   $98.45   $98.40  
  Purchase #5 $145.83   9.496%   $159.678   $159.68   $159.70   $159.70  
  Purchase #6 $37.92   6.627%   $40.433   $40.43   $40.45   $40.40  
  Purchase #7 $54.76   10.421%   $60.4665   $60.47   $60.45   $60.50  
  7 purchase totals = $798.38       $864.0669   $864.07   $864.10   $864.10