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 $62.27   9.746%   $68.3388   $68.34   $68.35   $68.30  
  Purchase #2 $88.93   5.420%   $93.75   $93.75   $93.75   $93.80  
  Purchase #3 $23.29   11.230%   $25.9055   $25.91   $25.90   $25.90  
  Purchase #4 $176.53   3.300%   $182.3555   $182.36   $182.35   $182.40  
  Purchase #5 $105.58   4.621%   $110.4589   $110.46   $110.45   $110.50  
  Purchase #6 $105.93   12.325%   $118.9859   $118.99   $119.00   $119.00  
  Purchase #7 $150.70   6.781%   $160.919   $160.92   $160.90   $160.90  
  7 purchase totals = $713.23       $760.7136   $760.73   $760.70   $760.80