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 $68.67   7.558%   $73.8601   $73.86   $73.85   $73.90  
  Purchase #2 $204.71   6.849%   $218.7306   $218.73   $218.75   $218.70  
  Purchase #3 $244.58   4.227%   $254.9184   $254.92   $254.90   $254.90  
  Purchase #4 $204.29   10.697%   $226.1429   $226.14   $226.15   $226.10  
  Purchase #5 $169.86   6.396%   $180.7242   $180.72   $180.70   $180.70  
  Purchase #6 $32.61   8.722%   $35.4542   $35.45   $35.45   $35.50  
  Purchase #7 $170.75   6.650%   $182.1049   $182.10   $182.10   $182.10  
  7 purchase totals = $1,095.47       $1,171.9353   $1,171.92   $1,171.90   $1,171.90