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 $107.84   6.152%   $114.4743   $114.47   $114.45   $114.50  
  Purchase #2 $211.33   4.168%   $220.1382   $220.14   $220.15   $220.10  
  Purchase #3 $34.32   4.631%   $35.9094   $35.91   $35.90   $35.90  
  Purchase #4 $84.94   6.117%   $90.1358   $90.14   $90.15   $90.10  
  Purchase #5 $132.26   10.599%   $146.2782   $146.28   $146.30   $146.30  
  Purchase #6 $189.95   5.185%   $199.7989   $199.80   $199.80   $199.80  
  Purchase #7 $230.55   9.773%   $253.0817   $253.08   $253.10   $253.10  
  7 purchase totals = $991.19       $1,059.8165   $1,059.82   $1,059.85   $1,059.80