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 $92.87   3.283%   $95.9189   $95.92   $95.90   $95.90  
  Purchase #2 $193.67   7.219%   $207.651   $207.65   $207.65   $207.70  
  Purchase #3 $215.62   9.448%   $235.9918   $235.99   $236.00   $236.00  
  Purchase #4 $40.48   8.839%   $44.058   $44.06   $44.05   $44.10  
  Purchase #5 $13.56   5.649%   $14.326   $14.33   $14.35   $14.30  
  Purchase #6 $233.50   8.457%   $253.2471   $253.25   $253.25   $253.20  
  Purchase #7 $139.33   10.537%   $154.0112   $154.01   $154.00   $154.00  
  7 purchase totals = $929.03       $1,005.2040   $1,005.21   $1,005.20   $1,005.20