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 $189.28   8.112%   $204.6344   $204.63   $204.65   $204.60  
  Purchase #2 $239.63   9.336%   $262.0019   $262.00   $262.00   $262.00  
  Purchase #3 $37.73   8.170%   $40.8125   $40.81   $40.80   $40.80  
  Purchase #4 $174.70   9.863%   $191.9307   $191.93   $191.95   $191.90  
  Purchase #5 $84.79   9.801%   $93.1003   $93.10   $93.10   $93.10  
  Purchase #6 $129.76   11.559%   $144.759   $144.76   $144.75   $144.80  
  Purchase #7 $83.48   9.611%   $91.5033   $91.50   $91.50   $91.50  
  7 purchase totals = $939.37       $1,028.7421   $1,028.73   $1,028.75   $1,028.70