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	$53.54	5.316%	$56.3862	$56.39	$56.40	$56.40
Purchase #2	$6.50	3.626%	$6.7357	$6.74	$6.75	$6.70
Purchase #3	$82.27	10.480%	$90.8919	$90.89	$90.90	$90.90
Purchase #4	$103.32	10.780%	$114.4579	$114.46	$114.45	$114.50
Purchase #5	$117.56	9.148%	$128.3144	$128.31	$128.30	$128.30
Purchase #6	$89.77	3.815%	$93.1947	$93.19	$93.20	$93.20
Purchase #7	$83.67	11.250%	$93.0829	$93.08	$93.10	$93.10
7 purchase totals =	$536.63		$583.0637	$583.06	$583.10	$583.10