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	$191.35	13.535%	$217.2492	$217.25	$217.25	$217.20
Purchase #2	$101.75	10.854%	$112.7939	$112.79	$112.80	$112.80
Purchase #3	$92.50	6.219%	$98.2526	$98.25	$98.25	$98.30
Purchase #4	$80.59	12.189%	$90.4131	$90.41	$90.40	$90.40
Purchase #5	$131.28	7.656%	$141.3308	$141.33	$141.35	$141.30
Purchase #6	$142.35	11.698%	$159.0021	$159.00	$159.00	$159.00
Purchase #7	$77.46	4.564%	$80.9953	$81.00	$81.00	$81.00
7 purchase totals =	$817.28		$900.0370	$900.03	$900.05	$900.00