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 $71.59   6.151%   $75.9935   $75.99   $76.00   $76.00  
  Purchase #2 $163.58   13.698%   $185.9872   $185.99   $186.00   $186.00  
  Purchase #3 $188.95   6.619%   $201.4566   $201.46   $201.45   $201.50  
  Purchase #4 $87.38   9.633%   $95.7973   $95.80   $95.80   $95.80  
  Purchase #5 $148.90   3.763%   $154.5031   $154.50   $154.50   $154.50  
  Purchase #6 $211.77   13.508%   $240.3759   $240.38   $240.40   $240.40  
  Purchase #7 $92.53   5.179%   $97.3221   $97.32   $97.30   $97.30  
  7 purchase totals = $964.70       $1,051.4357   $1,051.44   $1,051.45   $1,051.50