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 $248.52   6.557%   $264.8155   $264.82   $264.80   $264.80  
  Purchase #2 $158.86   12.588%   $178.8573   $178.86   $178.85   $178.90  
  Purchase #3 $116.34   7.357%   $124.8991   $124.90   $124.90   $124.90  
  Purchase #4 $46.86   9.795%   $51.4499   $51.45   $51.45   $51.40  
  Purchase #5 $88.67   4.462%   $92.6265   $92.63   $92.65   $92.60  
  Purchase #6 $15.28   13.734%   $17.3786   $17.38   $17.40   $17.40  
  Purchase #7 $147.56   5.747%   $156.0403   $156.04   $156.05   $156.00  
  7 purchase totals = $822.09       $886.0672   $886.08   $886.10   $886.00