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 $81.95   4.584%   $85.7066   $85.71   $85.70   $85.70  
  Purchase #2 $210.67   11.802%   $235.5333   $235.53   $235.55   $235.50  
  Purchase #3 $64.44   5.355%   $67.8908   $67.89   $67.90   $67.90  
  Purchase #4 $14.97   5.160%   $15.7425   $15.74   $15.75   $15.70  
  Purchase #5 $86.43   10.154%   $95.2061   $95.21   $95.20   $95.20  
  Purchase #6 $54.36   10.461%   $60.0466   $60.05   $60.05   $60.00  
  Purchase #7 $9.80   5.771%   $10.3656   $10.37   $10.35   $10.40  
  7 purchase totals = $522.62       $570.4915   $570.50   $570.50   $570.40