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	$243.51	5.562%	$257.054	$257.05	$257.05	$257.10
Purchase #2	$128.41	12.577%	$144.5601	$144.56	$144.55	$144.60
Purchase #3	$147.30	11.750%	$164.6078	$164.61	$164.60	$164.60
Purchase #4	$174.35	5.427%	$183.812	$183.81	$183.80	$183.80
Purchase #5	$215.64	10.520%	$238.3253	$238.33	$238.35	$238.30
Purchase #6	$82.49	10.399%	$91.0681	$91.07	$91.05	$91.10
Purchase #7	$83.64	10.782%	$92.6581	$92.66	$92.65	$92.70
7 purchase totals =	$1,075.34		$1,172.0854	$1,172.09	$1,172.05	$1,172.20