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 $106.39   12.239%   $119.4111   $119.41   $119.40   $119.40  
  Purchase #2 $195.36   8.871%   $212.6904   $212.69   $212.70   $212.70  
  Purchase #3 $116.85   8.359%   $126.6175   $126.62   $126.60   $126.60  
  Purchase #4 $10.92   10.294%   $12.0441   $12.04   $12.05   $12.00  
  Purchase #5 $167.40   6.797%   $178.7782   $178.78   $178.80   $178.80  
  Purchase #6 $241.75   7.634%   $260.2052   $260.21   $260.20   $260.20  
  Purchase #7 $120.59   4.514%   $126.0334   $126.03   $126.05   $126.00  
  7 purchase totals = $959.26       $1,035.7799   $1,035.78   $1,035.80   $1,035.70