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 $87.97   9.391%   $96.2313   $96.23   $96.25   $96.20  
  Purchase #2 $203.38   9.252%   $222.1967   $222.20   $222.20   $222.20  
  Purchase #3 $141.62   7.661%   $152.4695   $152.47   $152.45   $152.50  
  Purchase #4 $100.38   5.106%   $105.5054   $105.51   $105.50   $105.50  
  Purchase #5 $74.65   11.256%   $83.0526   $83.05   $83.05   $83.10  
  Purchase #6 $250.50   12.397%   $281.5545   $281.55   $281.55   $281.60  
  Purchase #7 $171.88   7.186%   $184.2313   $184.23   $184.25   $184.20  
  7 purchase totals = $1,030.38       $1,125.2413   $1,125.24   $1,125.25   $1,125.30