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 $245.47   12.364%   $275.8199   $275.82   $275.80   $275.80  
  Purchase #2 $175.34   11.378%   $195.2902   $195.29   $195.30   $195.30  
  Purchase #3 $178.42   4.331%   $186.1474   $186.15   $186.15   $186.10  
  Purchase #4 $217.64   12.764%   $245.4196   $245.42   $245.40   $245.40  
  Purchase #5 $225.88   4.368%   $235.7464   $235.75   $235.75   $235.70  
  Purchase #6 $55.32   8.529%   $60.0382   $60.04   $60.05   $60.00  
  Purchase #7 $190.29   4.322%   $198.5143   $198.51   $198.50   $198.50  
  7 purchase totals = $1,288.36       $1,396.9760   $1,396.98   $1,396.95   $1,396.80