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 $206.69   12.416%   $232.3526   $232.35   $232.35   $232.40  
  Purchase #2 $194.94   11.761%   $217.8669   $217.87   $217.85   $217.90  
  Purchase #3 $35.89   6.602%   $38.2595   $38.26   $38.25   $38.30  
  Purchase #4 $194.72   4.378%   $203.2448   $203.24   $203.25   $203.20  
  Purchase #5 $73.53   9.454%   $80.4815   $80.48   $80.50   $80.50  
  Purchase #6 $236.32   5.117%   $248.4125   $248.41   $248.40   $248.40  
  Purchase #7 $5.45   7.287%   $5.8471   $5.85   $5.85   $5.80  
  7 purchase totals = $947.54       $1,026.4649   $1,026.46   $1,026.45   $1,026.50