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 $183.62   8.760%   $199.7051   $199.71   $199.70   $199.70  
  Purchase #2 $226.80   11.585%   $253.0748   $253.07   $253.05   $253.10  
  Purchase #3 $249.40   11.552%   $278.2107   $278.21   $278.20   $278.20  
  Purchase #4 $151.30   11.605%   $168.8584   $168.86   $168.85   $168.90  
  Purchase #5 $46.66   4.249%   $48.6426   $48.64   $48.65   $48.60  
  Purchase #6 $177.58   13.819%   $202.1198   $202.12   $202.10   $202.10  
  Purchase #7 $130.35   11.486%   $145.322   $145.32   $145.30   $145.30  
  7 purchase totals = $1,165.71       $1,295.9334   $1,295.93   $1,295.85   $1,295.90