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 $61.78   6.782%   $65.9699   $65.97   $65.95   $66.00  
  Purchase #2 $180.37   8.351%   $195.4327   $195.43   $195.45   $195.40  
  Purchase #3 $70.38   10.364%   $77.6742   $77.67   $77.65   $77.70  
  Purchase #4 $8.57   7.342%   $9.1992   $9.20   $9.20   $9.20  
  Purchase #5 $43.27   13.545%   $49.1309   $49.13   $49.15   $49.10  
  Purchase #6 $20.51   5.171%   $21.5706   $21.57   $21.55   $21.60  
  Purchase #7 $111.96   13.671%   $127.2661   $127.27   $127.25   $127.30  
  7 purchase totals = $496.84       $546.2436   $546.24   $546.20   $546.30