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 $47.33   11.139%   $52.6021   $52.60   $52.60   $52.60  
  Purchase #2 $248.78   12.116%   $278.9222   $278.92   $278.90   $278.90  
  Purchase #3 $140.32   13.389%   $159.1074   $159.11   $159.10   $159.10  
  Purchase #4 $104.86   9.165%   $114.4704   $114.47   $114.45   $114.50  
  Purchase #5 $25.28   7.132%   $27.083   $27.08   $27.10   $27.10  
  Purchase #6 $116.99   3.292%   $120.8413   $120.84   $120.85   $120.80  
  Purchase #7 $244.63   11.521%   $272.8138   $272.81   $272.80   $272.80  
  7 purchase totals = $928.19       $1,025.8402   $1,025.83   $1,025.80   $1,025.80