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 $161.31   13.429%   $182.9723   $182.97   $182.95   $183.00  
  Purchase #2 $52.91   8.543%   $57.4301   $57.43   $57.45   $57.40  
  Purchase #3 $77.64   11.196%   $86.3326   $86.33   $86.35   $86.30  
  Purchase #4 $219.47   10.204%   $241.8647   $241.86   $241.85   $241.90  
  Purchase #5 $242.64   10.768%   $268.7675   $268.77   $268.75   $268.80  
  Purchase #6 $151.44   9.773%   $166.2402   $166.24   $166.25   $166.20  
  Purchase #7 $155.70   11.196%   $173.1322   $173.13   $173.15   $173.10  
  7 purchase totals = $1,061.11       $1,176.7396   $1,176.73   $1,176.75   $1,176.70