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 $183.49   10.706%   $203.1344   $203.13   $203.15   $203.10  
  Purchase #2 $159.65   8.459%   $173.1548   $173.15   $173.15   $173.20  
  Purchase #3 $26.25   7.316%   $28.1705   $28.17   $28.15   $28.20  
  Purchase #4 $33.69   7.450%   $36.1999   $36.20   $36.20   $36.20  
  Purchase #5 $63.89   11.484%   $71.2271   $71.23   $71.25   $71.20  
  Purchase #6 $151.68   9.442%   $166.0016   $166.00   $166.00   $166.00  
  Purchase #7 $68.72   9.773%   $75.436   $75.44   $75.45   $75.40  
  7 purchase totals = $687.37       $753.3243   $753.32   $753.35   $753.30