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 $152.39   13.677%   $173.2324   $173.23   $173.25   $173.20  
  Purchase #2 $199.58   6.539%   $212.6305   $212.63   $212.65   $212.60  
  Purchase #3 $204.73   5.398%   $215.7813   $215.78   $215.80   $215.80  
  Purchase #4 $147.29   13.523%   $167.208   $167.21   $167.20   $167.20  
  Purchase #5 $232.50   8.772%   $252.8949   $252.89   $252.90   $252.90  
  Purchase #6 $98.74   4.375%   $103.0599   $103.06   $103.05   $103.10  
  Purchase #7 $107.95   6.226%   $114.671   $114.67   $114.65   $114.70  
  7 purchase totals = $1,143.18       $1,239.4780   $1,239.47   $1,239.50   $1,239.50