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	$48.34	7.840%	$52.1299	$52.13	$52.15	$52.10
Purchase #2	$109.33	7.327%	$117.3406	$117.34	$117.35	$117.30
Purchase #3	$199.33	10.337%	$219.9347	$219.93	$219.95	$219.90
Purchase #4	$156.41	10.201%	$172.3654	$172.37	$172.35	$172.40
Purchase #5	$46.42	8.773%	$50.4924	$50.49	$50.50	$50.50
Purchase #6	$84.46	7.535%	$90.8241	$90.82	$90.80	$90.80
Purchase #7	$99.52	10.230%	$109.7009	$109.70	$109.70	$109.70
7 purchase totals =	$743.81		$812.7880	$812.78	$812.80	$812.70