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 $23.39   13.116%   $26.4578   $26.46   $26.45   $26.50  
  Purchase #2 $236.25   9.278%   $258.1693   $258.17   $258.15   $258.20  
  Purchase #3 $229.75   6.240%   $244.0864   $244.09   $244.10   $244.10  
  Purchase #4 $223.80   7.285%   $240.1038   $240.10   $240.10   $240.10  
  Purchase #5 $244.35   3.624%   $253.2052   $253.21   $253.20   $253.20  
  Purchase #6 $31.54   7.665%   $33.9575   $33.96   $33.95   $34.00  
  Purchase #7 $167.47   6.293%   $178.0089   $178.01   $178.00   $178.00  
  7 purchase totals = $1,156.55       $1,233.9889   $1,234.00   $1,233.95   $1,234.10