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 $96.62   5.124%   $101.5708   $101.57   $101.55   $101.60  
  Purchase #2 $164.77   5.809%   $174.3415   $174.34   $174.35   $174.30  
  Purchase #3 $8.78   12.770%   $9.9012   $9.90   $9.90   $9.90  
  Purchase #4 $24.37   10.487%   $26.9257   $26.93   $26.95   $26.90  
  Purchase #5 $175.88   10.366%   $194.1117   $194.11   $194.10   $194.10  
  Purchase #6 $176.80   8.602%   $192.0083   $192.01   $192.00   $192.00  
  Purchase #7 $27.97   9.294%   $30.5695   $30.57   $30.55   $30.60  
  7 purchase totals = $675.19       $729.4287   $729.43   $729.40   $729.40