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 $19.80   10.288%   $21.837   $21.84   $21.85   $21.80  
  Purchase #2 $171.92   10.160%   $189.3871   $189.39   $189.40   $189.40  
  Purchase #3 $182.94   5.522%   $193.0419   $193.04   $193.05   $193.00  
  Purchase #4 $220.95   4.326%   $230.5083   $230.51   $230.50   $230.50  
  Purchase #5 $160.93   13.110%   $182.0279   $182.03   $182.05   $182.00  
  Purchase #6 $19.67   8.227%   $21.2883   $21.29   $21.30   $21.30  
  Purchase #7 $182.45   12.547%   $205.342   $205.34   $205.35   $205.30  
  7 purchase totals = $958.66       $1,043.4325   $1,043.44   $1,043.50   $1,043.30