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 $150.37   12.536%   $169.2204   $169.22   $169.20   $169.20  
  Purchase #2 $104.38   13.659%   $118.6373   $118.64   $118.65   $118.60  
  Purchase #3 $240.77   12.591%   $271.0854   $271.09   $271.10   $271.10  
  Purchase #4 $246.57   12.108%   $276.4247   $276.42   $276.40   $276.40  
  Purchase #5 $73.65   11.241%   $81.929   $81.93   $81.95   $81.90  
  Purchase #6 $219.32   6.366%   $233.2819   $233.28   $233.30   $233.30  
  Purchase #7 $213.62   7.501%   $229.6436   $229.64   $229.65   $229.60  
  7 purchase totals = $1,248.68       $1,380.2223   $1,380.22   $1,380.25   $1,380.10