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 $185.81   12.665%   $209.3428   $209.34   $209.35   $209.30  
  Purchase #2 $65.42   3.433%   $67.6659   $67.67   $67.65   $67.70  
  Purchase #3 $107.91   7.743%   $116.2655   $116.27   $116.25   $116.30  
  Purchase #4 $235.99   13.130%   $266.9755   $266.98   $267.00   $267.00  
  Purchase #5 $118.77   13.141%   $134.3776   $134.38   $134.40   $134.40  
  Purchase #6 $177.30   8.567%   $192.4893   $192.49   $192.50   $192.50  
  Purchase #7 $152.58   8.662%   $165.7965   $165.80   $165.80   $165.80  
  7 purchase totals = $1,043.78       $1,152.9131   $1,152.93   $1,152.95   $1,153.00