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	$19.36	3.596%	$20.0562	$20.06	$20.05	$20.10
Purchase #2	$99.31	4.773%	$104.0501	$104.05	$104.05	$104.10
Purchase #3	$21.44	4.201%	$22.3407	$22.34	$22.35	$22.30
Purchase #4	$83.46	9.208%	$91.145	$91.15	$91.15	$91.10
Purchase #5	$199.75	13.655%	$227.0259	$227.03	$227.05	$227.00
Purchase #6	$57.63	3.856%	$59.8522	$59.85	$59.85	$59.90
Purchase #7	$119.44	12.215%	$134.0296	$134.03	$134.05	$134.00
7 purchase totals =	$600.39		$658.4997	$658.51	$658.55	$658.50