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 $6.74   3.304%   $6.9627   $6.96   $6.95   $7.00  
  Purchase #2 $136.49   6.441%   $145.2813   $145.28   $145.30   $145.30  
  Purchase #3 $183.92   13.844%   $209.3819   $209.38   $209.40   $209.40  
  Purchase #4 $166.31   7.520%   $178.8165   $178.82   $178.80   $178.80  
  Purchase #5 $234.65   3.167%   $242.0814   $242.08   $242.10   $242.10  
  Purchase #6 $143.63   9.120%   $156.7291   $156.73   $156.75   $156.70  
  Purchase #7 $210.64   10.664%   $233.1026   $233.10   $233.10   $233.10  
  7 purchase totals = $1,082.38       $1,172.3555   $1,172.35   $1,172.40   $1,172.40