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 $243.88   9.839%   $267.8754   $267.88   $267.90   $267.90  
  Purchase #2 $248.46   10.298%   $274.0464   $274.05   $274.05   $274.00  
  Purchase #3 $34.74   5.369%   $36.6052   $36.61   $36.60   $36.60  
  Purchase #4 $25.43   4.435%   $26.5578   $26.56   $26.55   $26.60  
  Purchase #5 $177.42   11.489%   $197.8038   $197.80   $197.80   $197.80  
  Purchase #6 $186.70   6.504%   $198.843   $198.84   $198.85   $198.80  
  Purchase #7 $102.45   7.211%   $109.8377   $109.84   $109.85   $109.80  
  7 purchase totals = $1,019.08       $1,111.5693   $1,111.58   $1,111.60   $1,111.50