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 $250.26   10.645%   $276.9002   $276.90   $276.90   $276.90  
  Purchase #2 $154.42   6.619%   $164.6411   $164.64   $164.65   $164.60  
  Purchase #3 $224.80   7.321%   $241.2576   $241.26   $241.25   $241.30  
  Purchase #4 $30.71   12.292%   $34.4849   $34.48   $34.50   $34.50  
  Purchase #5 $84.25   4.172%   $87.7649   $87.76   $87.75   $87.80  
  Purchase #6 $24.58   6.663%   $26.2178   $26.22   $26.20   $26.20  
  Purchase #7 $169.84   7.199%   $182.0668   $182.07   $182.05   $182.10  
  7 purchase totals = $938.86       $1,013.3333   $1,013.33   $1,013.30   $1,013.40