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 $244.38   13.197%   $276.6308   $276.63   $276.65   $276.60  
  Purchase #2 $196.58   12.203%   $220.5687   $220.57   $220.55   $220.60  
  Purchase #3 $5.44   11.331%   $6.0564   $6.06   $6.05   $6.10  
  Purchase #4 $163.94   6.588%   $174.7404   $174.74   $174.75   $174.70  
  Purchase #5 $55.95   6.475%   $59.5728   $59.57   $59.55   $59.60  
  Purchase #6 $146.51   13.387%   $166.1233   $166.12   $166.10   $166.10  
  Purchase #7 $240.28   4.187%   $250.3405   $250.34   $250.35   $250.30  
  7 purchase totals = $1,053.08       $1,154.0329   $1,154.03   $1,154.00   $1,154.00