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 $19.80   5.645%   $20.9177   $20.92   $20.90   $20.90  
  Purchase #2 $45.44   3.825%   $47.1781   $47.18   $47.20   $47.20  
  Purchase #3 $99.26   13.353%   $112.5142   $112.51   $112.50   $112.50  
  Purchase #4 $164.42   12.321%   $184.6782   $184.68   $184.70   $184.70  
  Purchase #5 $153.27   10.667%   $169.6193   $169.62   $169.60   $169.60  
  Purchase #6 $166.65   3.611%   $172.6677   $172.67   $172.65   $172.70  
  Purchase #7 $71.83   8.125%   $77.6662   $77.67   $77.65   $77.70  
  7 purchase totals = $720.67       $785.2414   $785.25   $785.20   $785.30