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 $88.38   7.532%   $95.0368   $95.04   $95.05   $95.00  
  Purchase #2 $70.33   9.491%   $77.005   $77.01   $77.00   $77.00  
  Purchase #3 $63.67   12.284%   $71.4912   $71.49   $71.50   $71.50  
  Purchase #4 $52.41   10.187%   $57.749   $57.75   $57.75   $57.70  
  Purchase #5 $49.31   6.195%   $52.3648   $52.36   $52.35   $52.40  
  Purchase #6 $95.91   8.685%   $104.2398   $104.24   $104.25   $104.20  
  Purchase #7 $52.45   6.683%   $55.9552   $55.96   $55.95   $56.00  
  7 purchase totals = $472.46       $513.8418   $513.85   $513.85   $513.80