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 $234.80   13.629%   $266.8009   $266.80   $266.80   $266.80  
  Purchase #2 $69.97   9.576%   $76.6703   $76.67   $76.65   $76.70  
  Purchase #3 $70.54   5.387%   $74.34   $74.34   $74.35   $74.30  
  Purchase #4 $200.51   7.441%   $215.4299   $215.43   $215.45   $215.40  
  Purchase #5 $110.47   6.714%   $117.887   $117.89   $117.90   $117.90  
  Purchase #6 $117.68   10.747%   $130.3271   $130.33   $130.35   $130.30  
  Purchase #7 $115.98   9.337%   $126.8091   $126.81   $126.80   $126.80  
  7 purchase totals = $919.95       $1,008.2643   $1,008.27   $1,008.30   $1,008.20