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 $151.42   12.151%   $169.819   $169.82   $169.80   $169.80  
  Purchase #2 $235.83   11.324%   $262.5354   $262.54   $262.55   $262.50  
  Purchase #3 $81.95   6.829%   $87.5464   $87.55   $87.55   $87.50  
  Purchase #4 $32.29   7.539%   $34.7243   $34.72   $34.70   $34.70  
  Purchase #5 $140.84   13.330%   $159.614   $159.61   $159.60   $159.60  
  Purchase #6 $153.45   10.250%   $169.1786   $169.18   $169.20   $169.20  
  Purchase #7 $32.30   9.206%   $35.2735   $35.27   $35.25   $35.30  
  7 purchase totals = $828.08       $918.6912   $918.69   $918.65   $918.60