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 $248.37   10.571%   $274.6252   $274.63   $274.65   $274.60  
  Purchase #2 $23.69   13.461%   $26.8789   $26.88   $26.90   $26.90  
  Purchase #3 $68.38   10.372%   $75.4724   $75.47   $75.45   $75.50  
  Purchase #4 $186.30   8.394%   $201.938   $201.94   $201.95   $201.90  
  Purchase #5 $247.49   10.128%   $272.5558   $272.56   $272.55   $272.60  
  Purchase #6 $191.94   6.806%   $205.0034   $205.00   $205.00   $205.00  
  Purchase #7 $197.32   6.276%   $209.7038   $209.70   $209.70   $209.70  
  7 purchase totals = $1,163.49       $1,266.1775   $1,266.18   $1,266.20   $1,266.20