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 $111.57   6.113%   $118.3903   $118.39   $118.40   $118.40  
  Purchase #2 $185.35   13.339%   $210.0738   $210.07   $210.05   $210.10  
  Purchase #3 $153.47   13.351%   $173.9598   $173.96   $173.95   $174.00  
  Purchase #4 $200.99   11.162%   $223.4245   $223.42   $223.40   $223.40  
  Purchase #5 $114.40   5.354%   $120.525   $120.53   $120.55   $120.50  
  Purchase #6 $147.46   8.649%   $160.2138   $160.21   $160.20   $160.20  
  Purchase #7 $91.27   3.802%   $94.7401   $94.74   $94.75   $94.70  
  7 purchase totals = $1,004.51       $1,101.3273   $1,101.32   $1,101.30   $1,101.30