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 $82.86   13.520%   $94.0627   $94.06   $94.05   $94.10  
  Purchase #2 $86.86   8.222%   $94.0016   $94.00   $94.00   $94.00  
  Purchase #3 $16.78   12.385%   $18.8582   $18.86   $18.85   $18.90  
  Purchase #4 $239.78   8.182%   $259.3988   $259.40   $259.40   $259.40  
  Purchase #5 $185.46   13.288%   $210.1039   $210.10   $210.10   $210.10  
  Purchase #6 $247.59   7.597%   $266.3994   $266.40   $266.40   $266.40  
  Purchase #7 $70.65   7.561%   $75.9918   $75.99   $76.00   $76.00  
  7 purchase totals = $929.98       $1,018.8164   $1,018.81   $1,018.80   $1,018.90