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	$6.76	7.719%	$7.2818	$7.28	$7.30	$7.30
Purchase #2	$116.63	11.762%	$130.348	$130.35	$130.35	$130.30
Purchase #3	$25.46	11.612%	$28.4164	$28.42	$28.40	$28.40
Purchase #4	$90.68	3.138%	$93.5255	$93.53	$93.55	$93.50
Purchase #5	$178.67	7.119%	$191.3895	$191.39	$191.40	$191.40
Purchase #6	$116.72	9.609%	$127.9356	$127.94	$127.95	$127.90
Purchase #7	$142.55	13.568%	$161.8912	$161.89	$161.90	$161.90
7 purchase totals =	$677.47		$740.7880	$740.80	$740.85	$740.70