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 $20.95   13.247%   $23.7252   $23.73   $23.75   $23.70  
  Purchase #2 $201.84   3.147%   $208.1919   $208.19   $208.20   $208.20  
  Purchase #3 $160.97   4.361%   $167.9899   $167.99   $168.00   $168.00  
  Purchase #4 $146.96   13.481%   $166.7717   $166.77   $166.75   $166.80  
  Purchase #5 $209.64   6.669%   $223.6209   $223.62   $223.60   $223.60  
  Purchase #6 $146.95   13.146%   $166.268   $166.27   $166.25   $166.30  
  Purchase #7 $119.36   5.799%   $126.2817   $126.28   $126.30   $126.30  
  7 purchase totals = $1,006.67       $1,082.8493   $1,082.85   $1,082.85   $1,082.90