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	$235.95	5.341%	$248.5521	$248.55	$248.55	$248.60
Purchase #2	$180.84	7.612%	$194.6055	$194.61	$194.60	$194.60
Purchase #3	$96.64	9.668%	$105.9832	$105.98	$106.00	$106.00
Purchase #4	$28.84	7.213%	$30.9202	$30.92	$30.90	$30.90
Purchase #5	$213.52	11.720%	$238.5445	$238.54	$238.55	$238.50
Purchase #6	$153.94	12.277%	$172.8392	$172.84	$172.85	$172.80
Purchase #7	$179.46	9.711%	$196.8874	$196.89	$196.90	$196.90
7 purchase totals =	$1,089.19		$1,188.3321	$1,188.33	$1,188.35	$1,188.30