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 $85.63   8.347%   $92.7775   $92.78   $92.80   $92.80  
  Purchase #2 $171.48   13.554%   $194.7224   $194.72   $194.70   $194.70  
  Purchase #3 $152.36   4.707%   $159.5316   $159.53   $159.55   $159.50  
  Purchase #4 $200.75   5.704%   $212.2008   $212.20   $212.20   $212.20  
  Purchase #5 $152.81   5.481%   $161.1855   $161.19   $161.20   $161.20  
  Purchase #6 $179.81   8.197%   $194.549   $194.55   $194.55   $194.50  
  Purchase #7 $113.89   13.466%   $129.2264   $129.23   $129.25   $129.20  
  7 purchase totals = $1,056.73       $1,144.1932   $1,144.20   $1,144.25   $1,144.10