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	$178.30	7.283%	$191.2856	$191.29	$191.30	$191.30
Purchase #2	$234.77	3.600%	$243.2217	$243.22	$243.20	$243.20
Purchase #3	$150.49	8.269%	$162.934	$162.93	$162.95	$162.90
Purchase #4	$49.63	13.674%	$56.4164	$56.42	$56.40	$56.40
Purchase #5	$191.57	7.218%	$205.3975	$205.40	$205.40	$205.40
Purchase #6	$86.76	3.114%	$89.4617	$89.46	$89.45	$89.50
Purchase #7	$40.86	4.864%	$42.8474	$42.85	$42.85	$42.80
7 purchase totals =	$932.38		$991.5643	$991.57	$991.55	$991.50