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 $243.47   13.751%   $276.9496   $276.95   $276.95   $276.90  
  Purchase #2 $168.99   3.653%   $175.1632   $175.16   $175.15   $175.20  
  Purchase #3 $44.46   6.279%   $47.2516   $47.25   $47.25   $47.30  
  Purchase #4 $120.63   13.696%   $137.1515   $137.15   $137.15   $137.20  
  Purchase #5 $101.64   6.784%   $108.5353   $108.54   $108.55   $108.50  
  Purchase #6 $59.96   10.663%   $66.3535   $66.35   $66.35   $66.40  
  Purchase #7 $198.29   5.343%   $208.8846   $208.88   $208.90   $208.90  
  7 purchase totals = $937.44       $1,020.2893   $1,020.28   $1,020.30   $1,020.40