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 $109.49   5.637%   $115.662   $115.66   $115.65   $115.70  
  Purchase #2 $69.27   12.739%   $78.0943   $78.09   $78.10   $78.10  
  Purchase #3 $70.87   11.701%   $79.1625   $79.16   $79.15   $79.20  
  Purchase #4 $205.47   4.550%   $214.8189   $214.82   $214.80   $214.80  
  Purchase #5 $243.97   4.204%   $254.2265   $254.23   $254.25   $254.20  
  Purchase #6 $180.85   3.566%   $187.2991   $187.30   $187.30   $187.30  
  Purchase #7 $148.97   7.705%   $160.4481   $160.45   $160.45   $160.40  
  7 purchase totals = $1,028.89       $1,089.7114   $1,089.71   $1,089.70   $1,089.70