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 $241.97   10.563%   $267.5293   $267.53   $267.55   $267.50  
  Purchase #2 $46.39   4.293%   $48.3815   $48.38   $48.40   $48.40  
  Purchase #3 $162.79   6.662%   $173.6351   $173.64   $173.65   $173.60  
  Purchase #4 $150.81   8.182%   $163.1493   $163.15   $163.15   $163.10  
  Purchase #5 $11.30   4.484%   $11.8067   $11.81   $11.80   $11.80  
  Purchase #6 $5.29   11.285%   $5.887   $5.89   $5.90   $5.90  
  Purchase #7 $231.28   8.111%   $250.0391   $250.04   $250.05   $250.00  
  7 purchase totals = $849.83       $920.4280   $920.44   $920.50   $920.30