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	$39.58	8.554%	$42.9657	$42.97	$42.95	$43.00
Purchase #2	$36.93	11.826%	$41.2973	$41.30	$41.30	$41.30
Purchase #3	$26.46	7.339%	$28.4019	$28.40	$28.40	$28.40
Purchase #4	$33.37	12.379%	$37.5009	$37.50	$37.50	$37.50
Purchase #5	$35.43	13.452%	$40.196	$40.20	$40.20	$40.20
Purchase #6	$244.52	3.815%	$253.8484	$253.85	$253.85	$253.80
Purchase #7	$69.79	3.545%	$72.2641	$72.26	$72.25	$72.30
7 purchase totals =	$486.08		$516.4743	$516.48	$516.45	$516.50