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 $235.63   11.509%   $262.7487   $262.75   $262.75   $262.70  
  Purchase #2 $156.83   5.233%   $165.0369   $165.04   $165.05   $165.00  
  Purchase #3 $65.54   3.568%   $67.8785   $67.88   $67.90   $67.90  
  Purchase #4 $64.93   4.835%   $68.0694   $68.07   $68.05   $68.10  
  Purchase #5 $207.56   6.487%   $221.0244   $221.02   $221.00   $221.00  
  Purchase #6 $69.37   9.462%   $75.9338   $75.93   $75.95   $75.90  
  Purchase #7 $214.53   12.174%   $240.6469   $240.65   $240.65   $240.60  
  7 purchase totals = $1,014.39       $1,101.3386   $1,101.34   $1,101.35   $1,101.20