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 $241.61   13.713%   $274.742   $274.74   $274.75   $274.70  
  Purchase #2 $223.30   10.157%   $245.9806   $245.98   $246.00   $246.00  
  Purchase #3 $56.27   6.277%   $59.8021   $59.80   $59.80   $59.80  
  Purchase #4 $39.84   5.439%   $42.0069   $42.01   $42.00   $42.00  
  Purchase #5 $125.80   12.618%   $141.6734   $141.67   $141.65   $141.70  
  Purchase #6 $169.45   7.655%   $182.4214   $182.42   $182.40   $182.40  
  Purchase #7 $243.54   7.610%   $262.0734   $262.07   $262.05   $262.10  
  7 purchase totals = $1,099.81       $1,208.6998   $1,208.69   $1,208.65   $1,208.70