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 $154.91   8.176%   $167.5754   $167.58   $167.60   $167.60  
  Purchase #2 $221.30   7.345%   $237.5545   $237.55   $237.55   $237.60  
  Purchase #3 $207.65   5.655%   $219.3926   $219.39   $219.40   $219.40  
  Purchase #4 $23.55   5.576%   $24.8631   $24.86   $24.85   $24.90  
  Purchase #5 $248.47   6.862%   $265.52   $265.52   $265.50   $265.50  
  Purchase #6 $200.93   12.548%   $226.1427   $226.14   $226.15   $226.10  
  Purchase #7 $234.30   11.794%   $261.9333   $261.93   $261.95   $261.90  
  7 purchase totals = $1,291.11       $1,402.9816   $1,402.97   $1,403.00   $1,403.00