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	$225.64	3.844%	$234.3136	$234.31	$234.30	$234.30
Purchase #2	$101.73	7.192%	$109.0464	$109.05	$109.05	$109.00
Purchase #3	$219.72	4.564%	$229.748	$229.75	$229.75	$229.70
Purchase #4	$49.76	5.740%	$52.6162	$52.62	$52.60	$52.60
Purchase #5	$149.30	7.174%	$160.0108	$160.01	$160.00	$160.00
Purchase #6	$60.42	12.264%	$67.8299	$67.83	$67.85	$67.80
Purchase #7	$80.58	10.610%	$89.1295	$89.13	$89.15	$89.10
7 purchase totals =	$887.15		$942.6944	$942.70	$942.70	$942.50