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 $23.61   5.591%   $24.93   $24.93   $24.95   $24.90  
  Purchase #2 $229.54   7.459%   $246.6614   $246.66   $246.65   $246.70  
  Purchase #3 $204.32   11.345%   $227.5001   $227.50   $227.50   $227.50  
  Purchase #4 $220.49   9.829%   $242.162   $242.16   $242.15   $242.20  
  Purchase #5 $154.68   9.448%   $169.2942   $169.29   $169.30   $169.30  
  Purchase #6 $50.37   5.634%   $53.2078   $53.21   $53.20   $53.20  
  Purchase #7 $214.49   3.289%   $221.5446   $221.54   $221.55   $221.50  
  7 purchase totals = $1,097.50       $1,185.3001   $1,185.29   $1,185.30   $1,185.30