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 $206.41   4.316%   $215.3187   $215.32   $215.30   $215.30  
  Purchase #2 $194.57   3.594%   $201.5628   $201.56   $201.55   $201.60  
  Purchase #3 $151.60   13.191%   $171.5976   $171.60   $171.60   $171.60  
  Purchase #4 $213.55   7.299%   $229.137   $229.14   $229.15   $229.10  
  Purchase #5 $10.90   11.567%   $12.1608   $12.16   $12.15   $12.20  
  Purchase #6 $224.62   6.633%   $239.519   $239.52   $239.50   $239.50  
  Purchase #7 $200.67   12.861%   $226.4782   $226.48   $226.50   $226.50  
  7 purchase totals = $1,202.32       $1,295.7741   $1,295.78   $1,295.75   $1,295.80