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 $248.84   11.110%   $276.4861   $276.49   $276.50   $276.50  
  Purchase #2 $132.44   5.445%   $139.6514   $139.65   $139.65   $139.70  
  Purchase #3 $203.35   10.785%   $225.2813   $225.28   $225.30   $225.30  
  Purchase #4 $6.86   6.657%   $7.3167   $7.32   $7.30   $7.30  
  Purchase #5 $31.48   13.815%   $35.829   $35.83   $35.85   $35.80  
  Purchase #6 $70.46   3.683%   $73.055   $73.06   $73.05   $73.10  
  Purchase #7 $7.86   9.496%   $8.6064   $8.61   $8.60   $8.60  
  7 purchase totals = $701.29       $766.2259   $766.24   $766.25   $766.30