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 $247.41   11.833%   $276.686   $276.69   $276.70   $276.70  
  Purchase #2 $26.64   4.126%   $27.7392   $27.74   $27.75   $27.70  
  Purchase #3 $91.66   13.332%   $103.8801   $103.88   $103.90   $103.90  
  Purchase #4 $216.65   9.846%   $237.9814   $237.98   $238.00   $238.00  
  Purchase #5 $112.46   12.719%   $126.7638   $126.76   $126.75   $126.80  
  Purchase #6 $61.26   4.359%   $63.9303   $63.93   $63.95   $63.90  
  Purchase #7 $180.37   3.836%   $187.289   $187.29   $187.30   $187.30  
  7 purchase totals = $936.45       $1,024.2698   $1,024.27   $1,024.35   $1,024.30