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 $246.63   5.526%   $260.2588   $260.26   $260.25   $260.30  
  Purchase #2 $102.46   3.500%   $106.0461   $106.05   $106.05   $106.00  
  Purchase #3 $115.49   9.159%   $126.0677   $126.07   $126.05   $126.10  
  Purchase #4 $124.99   7.572%   $134.4542   $134.45   $134.45   $134.50  
  Purchase #5 $190.51   6.382%   $202.6683   $202.67   $202.65   $202.70  
  Purchase #6 $51.29   4.786%   $53.7447   $53.74   $53.75   $53.70  
  Purchase #7 $140.50   12.502%   $158.0653   $158.07   $158.05   $158.10  
  7 purchase totals = $971.87       $1,041.3051   $1,041.31   $1,041.25   $1,041.40