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	$44.45	3.540%	$46.0235	$46.02	$46.00	$46.00
Purchase #2	$96.89	7.463%	$104.1209	$104.12	$104.10	$104.10
Purchase #3	$106.54	4.232%	$111.0488	$111.05	$111.05	$111.00
Purchase #4	$99.55	3.225%	$102.7605	$102.76	$102.75	$102.80
Purchase #5	$77.98	6.860%	$83.3294	$83.33	$83.35	$83.30
Purchase #6	$86.79	4.823%	$90.9759	$90.98	$91.00	$91.00
Purchase #7	$37.86	3.695%	$39.2589	$39.26	$39.25	$39.30
7 purchase totals =	$550.06		$577.5179	$577.52	$577.50	$577.50