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 $238.90   11.445%   $266.2421   $266.24   $266.25   $266.20  
  Purchase #2 $88.65   9.866%   $97.3962   $97.40   $97.40   $97.40  
  Purchase #3 $56.60   6.651%   $60.3645   $60.36   $60.35   $60.40  
  Purchase #4 $201.87   11.847%   $225.7855   $225.79   $225.80   $225.80  
  Purchase #5 $184.58   6.257%   $196.1292   $196.13   $196.15   $196.10  
  Purchase #6 $232.66   3.366%   $240.4913   $240.49   $240.50   $240.50  
  Purchase #7 $167.49   12.227%   $187.969   $187.97   $187.95   $188.00  
  7 purchase totals = $1,170.75       $1,274.3778   $1,274.38   $1,274.40   $1,274.40