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 $211.99   13.799%   $241.2425   $241.24   $241.25   $241.20  
  Purchase #2 $164.39   8.154%   $177.7944   $177.79   $177.80   $177.80  
  Purchase #3 $234.93   8.189%   $254.1684   $254.17   $254.15   $254.20  
  Purchase #4 $24.92   4.623%   $26.0721   $26.07   $26.05   $26.10  
  Purchase #5 $130.47   6.447%   $138.8814   $138.88   $138.90   $138.90  
  Purchase #6 $213.49   3.394%   $220.7359   $220.74   $220.75   $220.70  
  Purchase #7 $147.92   12.234%   $166.0165   $166.02   $166.00   $166.00  
  7 purchase totals = $1,128.11       $1,224.9112   $1,224.91   $1,224.90   $1,224.90