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 $244.96   6.591%   $261.1053   $261.11   $261.10   $261.10  
  Purchase #2 $156.52   11.780%   $174.9581   $174.96   $174.95   $175.00  
  Purchase #3 $100.89   6.839%   $107.7899   $107.79   $107.80   $107.80  
  Purchase #4 $221.40   12.463%   $248.9931   $248.99   $249.00   $249.00  
  Purchase #5 $98.76   3.436%   $102.1534   $102.15   $102.15   $102.20  
  Purchase #6 $82.43   7.177%   $88.346   $88.35   $88.35   $88.30  
  Purchase #7 $249.98   13.389%   $283.4498   $283.45   $283.45   $283.40  
  7 purchase totals = $1,154.94       $1,266.7956   $1,266.80   $1,266.80   $1,266.80