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 $61.89   11.530%   $69.0259   $69.03   $69.05   $69.00  
  Purchase #2 $247.54   8.857%   $269.4646   $269.46   $269.45   $269.50  
  Purchase #3 $84.54   10.477%   $93.3973   $93.40   $93.40   $93.40  
  Purchase #4 $54.79   10.274%   $60.4191   $60.42   $60.40   $60.40  
  Purchase #5 $47.40   12.296%   $53.2283   $53.23   $53.25   $53.20  
  Purchase #6 $94.69   12.555%   $106.5783   $106.58   $106.60   $106.60  
  Purchase #7 $186.80   12.249%   $209.6811   $209.68   $209.70   $209.70  
  7 purchase totals = $777.65       $861.7946   $861.80   $861.85   $861.80