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 $192.39   13.813%   $218.9648   $218.96   $218.95   $219.00  
  Purchase #2 $33.39   8.796%   $36.327   $36.33   $36.35   $36.30  
  Purchase #3 $143.39   8.822%   $156.0399   $156.04   $156.05   $156.00  
  Purchase #4 $103.31   8.714%   $112.3124   $112.31   $112.30   $112.30  
  Purchase #5 $159.68   9.692%   $175.1562   $175.16   $175.15   $175.20  
  Purchase #6 $156.74   7.412%   $168.3576   $168.36   $168.35   $168.40  
  Purchase #7 $85.74   7.307%   $92.005   $92.01   $92.00   $92.00  
  7 purchase totals = $874.64       $959.1629   $959.17   $959.15   $959.20