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 $126.69   6.719%   $135.2023   $135.20   $135.20   $135.20  
  Purchase #2 $207.26   9.335%   $226.6077   $226.61   $226.60   $226.60  
  Purchase #3 $161.69   8.193%   $174.9373   $174.94   $174.95   $174.90  
  Purchase #4 $226.98   6.616%   $241.997   $242.00   $242.00   $242.00  
  Purchase #5 $82.67   3.113%   $85.2435   $85.24   $85.25   $85.20  
  Purchase #6 $167.36   12.457%   $188.208   $188.21   $188.20   $188.20  
  Purchase #7 $244.96   3.606%   $253.7933   $253.79   $253.80   $253.80  
  7 purchase totals = $1,217.61       $1,305.9891   $1,305.99   $1,306.00   $1,305.90