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	$103.44	10.596%	$114.4005	$114.40	$114.40	$114.40
Purchase #2	$114.91	12.424%	$129.1864	$129.19	$129.20	$129.20
Purchase #3	$93.50	11.620%	$104.3647	$104.36	$104.35	$104.40
Purchase #4	$141.31	7.383%	$151.7429	$151.74	$151.75	$151.70
Purchase #5	$37.46	3.838%	$38.8977	$38.90	$38.90	$38.90
Purchase #6	$83.52	9.214%	$91.2155	$91.22	$91.20	$91.20
Purchase #7	$34.32	10.444%	$37.9044	$37.90	$37.90	$37.90
7 purchase totals =	$608.46		$667.7121	$667.71	$667.70	$667.70