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 $86.42   11.255%   $96.1466   $96.15   $96.15   $96.10  
  Purchase #2 $125.37   8.630%   $136.1894   $136.19   $136.20   $136.20  
  Purchase #3 $98.82   6.822%   $105.5615   $105.56   $105.55   $105.60  
  Purchase #4 $162.29   10.586%   $179.47   $179.47   $179.45   $179.50  
  Purchase #5 $121.62   3.109%   $125.4012   $125.40   $125.40   $125.40  
  Purchase #6 $124.26   10.540%   $137.357   $137.36   $137.35   $137.40  
  Purchase #7 $92.82   3.582%   $96.1448   $96.14   $96.15   $96.10  
  7 purchase totals = $811.60       $876.2705   $876.27   $876.25   $876.30