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	$115.77	11.277%	$128.8254	$128.83	$128.85	$128.80
Purchase #2	$240.63	3.581%	$249.247	$249.25	$249.25	$249.20
Purchase #3	$179.25	6.147%	$190.2685	$190.27	$190.25	$190.30
Purchase #4	$127.93	12.783%	$144.2833	$144.28	$144.30	$144.30
Purchase #5	$215.47	9.412%	$235.75	$235.75	$235.75	$235.80
Purchase #6	$67.91	7.693%	$73.1343	$73.13	$73.15	$73.10
Purchase #7	$172.71	13.618%	$196.2296	$196.23	$196.25	$196.20
7 purchase totals =	$1,119.67		$1,217.7381	$1,217.74	$1,217.80	$1,217.70