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 $198.96   7.361%   $213.6054   $213.61   $213.60   $213.60  
  Purchase #2 $111.62   6.563%   $118.9456   $118.95   $118.95   $118.90  
  Purchase #3 $155.83   6.520%   $165.9901   $165.99   $166.00   $166.00  
  Purchase #4 $240.86   8.506%   $261.3476   $261.35   $261.35   $261.30  
  Purchase #5 $150.77   3.396%   $155.8901   $155.89   $155.90   $155.90  
  Purchase #6 $148.75   11.183%   $165.3847   $165.38   $165.40   $165.40  
  Purchase #7 $185.27   13.839%   $210.9095   $210.91   $210.90   $210.90  
  7 purchase totals = $1,192.06       $1,292.0730   $1,292.08   $1,292.10   $1,292.00