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 $242.38   10.605%   $268.0844   $268.08   $268.10   $268.10  
  Purchase #2 $216.62   11.519%   $241.5725   $241.57   $241.55   $241.60  
  Purchase #3 $153.82   12.492%   $173.0352   $173.04   $173.05   $173.00  
  Purchase #4 $8.43   4.717%   $8.8276   $8.83   $8.85   $8.80  
  Purchase #5 $236.49   8.409%   $256.3764   $256.38   $256.40   $256.40  
  Purchase #6 $157.26   7.609%   $169.2259   $169.23   $169.25   $169.20  
  Purchase #7 $17.93   6.196%   $19.0409   $19.04   $19.05   $19.00  
  7 purchase totals = $1,032.93       $1,136.1629   $1,136.17   $1,136.25   $1,136.10