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 $246.73   9.173%   $269.3625   $269.36   $269.35   $269.40  
  Purchase #2 $213.72   13.235%   $242.0058   $242.01   $242.00   $242.00  
  Purchase #3 $224.91   9.291%   $245.8064   $245.81   $245.80   $245.80  
  Purchase #4 $227.77   4.210%   $237.3591   $237.36   $237.35   $237.40  
  Purchase #5 $40.73   9.205%   $44.4792   $44.48   $44.50   $44.50  
  Purchase #6 $126.79   5.132%   $133.2969   $133.30   $133.30   $133.30  
  Purchase #7 $77.59   4.595%   $81.1553   $81.16   $81.15   $81.20  
  7 purchase totals = $1,158.24       $1,253.4652   $1,253.48   $1,253.45   $1,253.60