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 $85.42   9.153%   $93.2385   $93.24   $93.25   $93.20  
  Purchase #2 $209.93   11.359%   $233.7759   $233.78   $233.80   $233.80  
  Purchase #3 $54.73   5.479%   $57.7287   $57.73   $57.75   $57.70  
  Purchase #4 $241.97   7.262%   $259.5419   $259.54   $259.55   $259.50  
  Purchase #5 $110.68   5.743%   $117.0364   $117.04   $117.05   $117.00  
  Purchase #6 $148.83   3.747%   $154.4067   $154.41   $154.40   $154.40  
  Purchase #7 $123.43   4.714%   $129.2485   $129.25   $129.25   $129.20  
  7 purchase totals = $974.99       $1,044.9766   $1,044.99   $1,045.05   $1,044.80