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 $245.58   12.270%   $275.7127   $275.71   $275.70   $275.70  
  Purchase #2 $98.71   7.585%   $106.1972   $106.20   $106.20   $106.20  
  Purchase #3 $177.96   5.725%   $188.1482   $188.15   $188.15   $188.10  
  Purchase #4 $59.74   12.519%   $67.2189   $67.22   $67.20   $67.20  
  Purchase #5 $124.96   4.760%   $130.9081   $130.91   $130.90   $130.90  
  Purchase #6 $22.49   5.333%   $23.6894   $23.69   $23.70   $23.70  
  Purchase #7 $225.88   10.647%   $249.9294   $249.93   $249.95   $249.90  
  7 purchase totals = $955.32       $1,041.8039   $1,041.81   $1,041.80   $1,041.70