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 $58.55   5.558%   $61.8042   $61.80   $61.80   $61.80  
  Purchase #2 $164.34   7.479%   $176.631   $176.63   $176.65   $176.60  
  Purchase #3 $227.97   12.139%   $255.6433   $255.64   $255.65   $255.60  
  Purchase #4 $136.33   9.239%   $148.9255   $148.93   $148.95   $148.90  
  Purchase #5 $240.94   4.132%   $250.8956   $250.90   $250.90   $250.90  
  Purchase #6 $244.95   9.247%   $267.6005   $267.60   $267.60   $267.60  
  Purchase #7 $150.48   13.418%   $170.6714   $170.67   $170.65   $170.70  
  7 purchase totals = $1,223.56       $1,332.1715   $1,332.17   $1,332.20   $1,332.10