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 $126.89   7.345%   $136.2101   $136.21   $136.20   $136.20  
  Purchase #2 $8.94   9.825%   $9.8184   $9.82   $9.80   $9.80  
  Purchase #3 $149.94   13.774%   $170.5927   $170.59   $170.60   $170.60  
  Purchase #4 $29.44   13.311%   $33.3588   $33.36   $33.35   $33.40  
  Purchase #5 $55.54   4.172%   $57.8571   $57.86   $57.85   $57.90  
  Purchase #6 $164.86   8.831%   $179.4188   $179.42   $179.40   $179.40  
  Purchase #7 $24.46   11.826%   $27.3526   $27.35   $27.35   $27.40  
  7 purchase totals = $560.07       $614.6085   $614.61   $614.55   $614.70