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 $24.86   7.262%   $26.6653   $26.67   $26.65   $26.70  
  Purchase #2 $98.80   11.265%   $109.9298   $109.93   $109.95   $109.90  
  Purchase #3 $157.93   7.728%   $170.1348   $170.13   $170.15   $170.10  
  Purchase #4 $164.61   6.643%   $175.545   $175.55   $175.55   $175.50  
  Purchase #5 $18.51   12.187%   $20.7658   $20.77   $20.75   $20.80  
  Purchase #6 $159.55   4.547%   $166.8047   $166.80   $166.80   $166.80  
  Purchase #7 $59.40   5.702%   $62.787   $62.79   $62.80   $62.80  
  7 purchase totals = $683.66       $732.6324   $732.64   $732.65   $732.60