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 $70.51   9.480%   $77.1943   $77.19   $77.20   $77.20  
  Purchase #2 $190.95   3.785%   $198.1775   $198.18   $198.20   $198.20  
  Purchase #3 $124.34   8.529%   $134.945   $134.95   $134.95   $134.90  
  Purchase #4 $60.27   13.211%   $68.2323   $68.23   $68.25   $68.20  
  Purchase #5 $132.76   12.509%   $149.3669   $149.37   $149.35   $149.40  
  Purchase #6 $207.59   7.278%   $222.6984   $222.70   $222.70   $222.70  
  Purchase #7 $241.60   13.198%   $273.4864   $273.49   $273.50   $273.50  
  7 purchase totals = $1,028.02       $1,124.1008   $1,124.11   $1,124.15   $1,124.10