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 $207.63   8.106%   $224.4605   $224.46   $224.45   $224.50  
  Purchase #2 $153.91   6.148%   $163.3724   $163.37   $163.35   $163.40  
  Purchase #3 $30.73   3.155%   $31.6995   $31.70   $31.70   $31.70  
  Purchase #4 $76.58   6.441%   $81.5125   $81.51   $81.50   $81.50  
  Purchase #5 $94.52   7.133%   $101.2621   $101.26   $101.25   $101.30  
  Purchase #6 $184.86   5.319%   $194.6927   $194.69   $194.70   $194.70  
  Purchase #7 $239.81   11.703%   $267.875   $267.88   $267.90   $267.90  
  7 purchase totals = $988.04       $1,064.8747   $1,064.87   $1,064.85   $1,065.00