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 $212.37   5.869%   $224.834   $224.83   $224.85   $224.80  
  Purchase #2 $74.43   7.151%   $79.7525   $79.75   $79.75   $79.80  
  Purchase #3 $58.55   4.467%   $61.1654   $61.17   $61.15   $61.20  
  Purchase #4 $97.61   7.433%   $104.8654   $104.87   $104.85   $104.90  
  Purchase #5 $72.90   3.246%   $75.2663   $75.27   $75.25   $75.30  
  Purchase #6 $59.36   10.165%   $65.3939   $65.39   $65.40   $65.40  
  Purchase #7 $138.38   5.798%   $146.4033   $146.40   $146.40   $146.40  
  7 purchase totals = $713.60       $757.6808   $757.68   $757.65   $757.80