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	$52.60	9.734%	$57.7201	$57.72	$57.70	$57.70
Purchase #2	$217.36	12.612%	$244.7734	$244.77	$244.75	$244.80
Purchase #3	$66.96	9.539%	$73.3473	$73.35	$73.35	$73.30
Purchase #4	$126.38	5.454%	$133.2728	$133.27	$133.25	$133.30
Purchase #5	$77.79	5.801%	$82.3026	$82.30	$82.30	$82.30
Purchase #6	$224.76	13.244%	$254.5272	$254.53	$254.55	$254.50
Purchase #7	$86.65	3.734%	$89.8855	$89.89	$89.90	$89.90
7 purchase totals =	$852.50		$935.8289	$935.83	$935.80	$935.80