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 $105.72   9.723%   $115.9992   $116.00   $116.00   $116.00  
  Purchase #2 $205.71   6.375%   $218.824   $218.82   $218.80   $218.80  
  Purchase #3 $221.26   12.470%   $248.8511   $248.85   $248.85   $248.90  
  Purchase #4 $248.42   3.119%   $256.1682   $256.17   $256.15   $256.20  
  Purchase #5 $90.42   10.665%   $100.0633   $100.06   $100.05   $100.10  
  Purchase #6 $227.39   6.603%   $242.4046   $242.40   $242.40   $242.40  
  Purchase #7 $110.86   13.156%   $125.4447   $125.44   $125.45   $125.40  
  7 purchase totals = $1,209.78       $1,307.7551   $1,307.74   $1,307.70   $1,307.80