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 $189.34   9.822%   $207.937   $207.94   $207.95   $207.90  
  Purchase #2 $174.93   5.866%   $185.1914   $185.19   $185.20   $185.20  
  Purchase #3 $68.27   13.798%   $77.6899   $77.69   $77.70   $77.70  
  Purchase #4 $25.59   5.622%   $27.0287   $27.03   $27.05   $27.00  
  Purchase #5 $142.78   9.429%   $156.2427   $156.24   $156.25   $156.20  
  Purchase #6 $239.60   12.124%   $268.6491   $268.65   $268.65   $268.60  
  Purchase #7 $31.30   6.650%   $33.3815   $33.38   $33.40   $33.40  
  7 purchase totals = $871.81       $956.1203   $956.12   $956.20   $956.00