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 $63.47   13.310%   $71.9179   $71.92   $71.90   $71.90  
  Purchase #2 $212.92   6.333%   $226.4042   $226.40   $226.40   $226.40  
  Purchase #3 $181.93   8.706%   $197.7688   $197.77   $197.75   $197.80  
  Purchase #4 $246.75   9.571%   $270.3664   $270.37   $270.35   $270.40  
  Purchase #5 $39.50   7.869%   $42.6083   $42.61   $42.60   $42.60  
  Purchase #6 $24.39   9.165%   $26.6253   $26.63   $26.65   $26.60  
  Purchase #7 $250.73   3.497%   $259.498   $259.50   $259.50   $259.50  
  7 purchase totals = $1,019.69       $1,095.1889   $1,095.20   $1,095.15   $1,095.20