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 $87.86   12.338%   $98.7002   $98.70   $98.70   $98.70  
  Purchase #2 $225.36   5.708%   $238.2235   $238.22   $238.20   $238.20  
  Purchase #3 $17.73   4.698%   $18.563   $18.56   $18.55   $18.60  
  Purchase #4 $62.53   11.371%   $69.6403   $69.64   $69.65   $69.60  
  Purchase #5 $75.41   13.325%   $85.4584   $85.46   $85.45   $85.50  
  Purchase #6 $246.64   8.178%   $266.8102   $266.81   $266.80   $266.80  
  Purchase #7 $238.55   8.578%   $259.0128   $259.01   $259.00   $259.00  
  7 purchase totals = $954.08       $1,036.4084   $1,036.40   $1,036.35   $1,036.40