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 $68.51   7.155%   $73.4119   $73.41   $73.40   $73.40  
  Purchase #2 $216.86   8.330%   $234.9244   $234.92   $234.90   $234.90  
  Purchase #3 $137.83   10.862%   $152.8011   $152.80   $152.80   $152.80  
  Purchase #4 $41.64   7.419%   $44.7293   $44.73   $44.75   $44.70  
  Purchase #5 $244.71   8.361%   $265.1702   $265.17   $265.15   $265.20  
  Purchase #6 $100.66   9.345%   $110.0667   $110.07   $110.05   $110.10  
  Purchase #7 $166.66   6.510%   $177.5096   $177.51   $177.50   $177.50  
  7 purchase totals = $976.87       $1,058.6132   $1,058.61   $1,058.55   $1,058.60