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 $169.47   13.263%   $191.9468   $191.95   $191.95   $191.90  
  Purchase #2 $21.91   10.515%   $24.2138   $24.21   $24.20   $24.20  
  Purchase #3 $233.82   5.593%   $246.8976   $246.90   $246.90   $246.90  
  Purchase #4 $120.44   11.509%   $134.3014   $134.30   $134.30   $134.30  
  Purchase #5 $152.62   9.334%   $166.8656   $166.87   $166.85   $166.90  
  Purchase #6 $30.40   8.154%   $32.8788   $32.88   $32.90   $32.90  
  Purchase #7 $85.46   13.698%   $97.1663   $97.17   $97.15   $97.20  
  7 purchase totals = $814.12       $894.2703   $894.28   $894.25   $894.30