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	$50.63	12.542%	$56.98	$56.98	$57.00	$57.00
Purchase #2	$165.49	4.270%	$172.5564	$172.56	$172.55	$172.60
Purchase #3	$14.96	8.874%	$16.2876	$16.29	$16.30	$16.30
Purchase #4	$124.77	13.664%	$141.8186	$141.82	$141.80	$141.80
Purchase #5	$70.42	4.465%	$73.5643	$73.56	$73.55	$73.60
Purchase #6	$150.39	10.106%	$165.5884	$165.59	$165.60	$165.60
Purchase #7	$145.99	13.649%	$165.9162	$165.92	$165.90	$165.90
7 purchase totals =	$722.65		$792.7115	$792.72	$792.70	$792.80