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 $7.66   7.205%   $8.2119   $8.21   $8.20   $8.20  
  Purchase #2 $156.57   12.378%   $175.9502   $175.95   $175.95   $176.00  
  Purchase #3 $19.67   9.201%   $21.4798   $21.48   $21.50   $21.50  
  Purchase #4 $151.63   13.164%   $171.5906   $171.59   $171.60   $171.60  
  Purchase #5 $145.76   4.616%   $152.4883   $152.49   $152.50   $152.50  
  Purchase #6 $70.41   4.707%   $73.7242   $73.72   $73.70   $73.70  
  Purchase #7 $64.74   13.616%   $73.555   $73.56   $73.55   $73.60  
  7 purchase totals = $616.44       $677.0000   $677.00   $677.00   $677.10