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 $230.85   13.804%   $262.7165   $262.72   $262.70   $262.70  
  Purchase #2 $43.45   3.237%   $44.8565   $44.86   $44.85   $44.90  
  Purchase #3 $169.74   10.190%   $187.0365   $187.04   $187.05   $187.00  
  Purchase #4 $25.29   4.820%   $26.509   $26.51   $26.50   $26.50  
  Purchase #5 $59.97   3.436%   $62.0306   $62.03   $62.05   $62.00  
  Purchase #6 $115.87   7.666%   $124.7526   $124.75   $124.75   $124.80  
  Purchase #7 $234.53   13.580%   $266.3792   $266.38   $266.40   $266.40  
  7 purchase totals = $879.70       $974.2809   $974.29   $974.30   $974.30