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 $67.48   8.565%   $73.2597   $73.26   $73.25   $73.30  
  Purchase #2 $190.53   5.682%   $201.3559   $201.36   $201.35   $201.40  
  Purchase #3 $158.25   13.111%   $178.9982   $179.00   $179.00   $179.00  
  Purchase #4 $148.85   3.282%   $153.7353   $153.74   $153.75   $153.70  
  Purchase #5 $51.32   7.228%   $55.0294   $55.03   $55.05   $55.00  
  Purchase #6 $210.58   12.341%   $236.5677   $236.57   $236.55   $236.60  
  Purchase #7 $144.64   9.635%   $158.5761   $158.58   $158.60   $158.60  
  7 purchase totals = $971.65       $1,057.5223   $1,057.54   $1,057.55   $1,057.60