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 $203.48   10.218%   $224.2716   $224.27   $224.25   $224.30  
  Purchase #2 $187.48   8.822%   $204.0195   $204.02   $204.00   $204.00  
  Purchase #3 $106.25   7.228%   $113.9298   $113.93   $113.95   $113.90  
  Purchase #4 $122.63   8.609%   $133.1872   $133.19   $133.20   $133.20  
  Purchase #5 $247.33   10.577%   $273.4901   $273.49   $273.50   $273.50  
  Purchase #6 $62.75   12.644%   $70.6841   $70.68   $70.70   $70.70  
  Purchase #7 $42.90   7.279%   $46.0227   $46.02   $46.00   $46.00  
  7 purchase totals = $972.82       $1,065.6050   $1,065.60   $1,065.60   $1,065.60