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	$89.91	7.781%	$96.9059	$96.91	$96.90	$96.90
Purchase #2	$132.86	10.129%	$146.3174	$146.32	$146.30	$146.30
Purchase #3	$166.58	10.835%	$184.6289	$184.63	$184.65	$184.60
Purchase #4	$71.84	3.753%	$74.5362	$74.54	$74.55	$74.50
Purchase #5	$211.88	12.373%	$238.0959	$238.10	$238.10	$238.10
Purchase #6	$106.25	3.418%	$109.8816	$109.88	$109.90	$109.90
Purchase #7	$42.29	13.555%	$48.0224	$48.02	$48.00	$48.00
7 purchase totals =	$821.61		$898.3883	$898.40	$898.40	$898.30