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 $69.86   9.158%   $76.2578   $76.26   $76.25   $76.30  
  Purchase #2 $173.72   10.396%   $191.7799   $191.78   $191.80   $191.80  
  Purchase #3 $197.83   9.741%   $217.1006   $217.10   $217.10   $217.10  
  Purchase #4 $230.54   8.159%   $249.3498   $249.35   $249.35   $249.30  
  Purchase #5 $209.71   13.474%   $237.9663   $237.97   $237.95   $238.00  
  Purchase #6 $122.71   10.353%   $135.4142   $135.41   $135.40   $135.40  
  Purchase #7 $155.30   5.381%   $163.6567   $163.66   $163.65   $163.70  
  7 purchase totals = $1,159.67       $1,271.5253   $1,271.53   $1,271.50   $1,271.60