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 $173.83   10.717%   $192.4594   $192.46   $192.45   $192.50  
  Purchase #2 $153.91   9.724%   $168.8762   $168.88   $168.90   $168.90  
  Purchase #3 $226.39   3.496%   $234.3046   $234.30   $234.30   $234.30  
  Purchase #4 $157.43   11.606%   $175.7013   $175.70   $175.70   $175.70  
  Purchase #5 $149.97   5.605%   $158.3758   $158.38   $158.40   $158.40  
  Purchase #6 $189.40   12.287%   $212.6716   $212.67   $212.65   $212.70  
  Purchase #7 $215.26   4.476%   $224.895   $224.90   $224.90   $224.90  
  7 purchase totals = $1,266.19       $1,367.2839   $1,367.29   $1,367.30   $1,367.40