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	$37.51	12.650%	$42.255	$42.26	$42.25	$42.30
Purchase #2	$32.56	3.546%	$33.7146	$33.71	$33.70	$33.70
Purchase #3	$66.27	6.124%	$70.3284	$70.33	$70.35	$70.30
Purchase #4	$76.83	4.124%	$79.9985	$80.00	$80.00	$80.00
Purchase #5	$187.72	3.750%	$194.7595	$194.76	$194.75	$194.80
Purchase #6	$177.73	12.827%	$200.5274	$200.53	$200.55	$200.50
Purchase #7	$225.72	3.365%	$233.3155	$233.32	$233.30	$233.30
7 purchase totals =	$804.34		$854.8989	$854.91	$854.90	$854.90