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 $24.84   6.328%   $26.4119   $26.41   $26.40   $26.40  
  Purchase #2 $110.42   5.860%   $116.8906   $116.89   $116.90   $116.90  
  Purchase #3 $59.29   4.696%   $62.0743   $62.07   $62.05   $62.10  
  Purchase #4 $16.70   12.578%   $18.8005   $18.80   $18.80   $18.80  
  Purchase #5 $248.33   7.176%   $266.1502   $266.15   $266.15   $266.20  
  Purchase #6 $248.95   6.253%   $264.5168   $264.52   $264.50   $264.50  
  Purchase #7 $160.54   6.719%   $171.3267   $171.33   $171.35   $171.30  
  7 purchase totals = $869.07       $926.1710   $926.17   $926.15   $926.20