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 $246.97   6.740%   $263.6158   $263.62   $263.60   $263.60  
  Purchase #2 $85.51   9.307%   $93.4684   $93.47   $93.45   $93.50  
  Purchase #3 $40.90   4.369%   $42.6869   $42.69   $42.70   $42.70  
  Purchase #4 $242.63   12.385%   $272.6797   $272.68   $272.70   $272.70  
  Purchase #5 $119.92   4.581%   $125.4135   $125.41   $125.40   $125.40  
  Purchase #6 $109.52   5.286%   $115.3092   $115.31   $115.30   $115.30  
  Purchase #7 $50.59   3.282%   $52.2504   $52.25   $52.25   $52.30  
  7 purchase totals = $896.04       $965.4239   $965.43   $965.40   $965.50