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	$83.54	5.426%	$88.0729	$88.07	$88.05	$88.10
Purchase #2	$45.33	13.378%	$51.3942	$51.39	$51.40	$51.40
Purchase #3	$96.82	4.730%	$101.3996	$101.40	$101.40	$101.40
Purchase #4	$113.46	9.695%	$124.4599	$124.46	$124.45	$124.50
Purchase #5	$35.52	11.221%	$39.5057	$39.51	$39.50	$39.50
Purchase #6	$175.94	7.670%	$189.4346	$189.43	$189.45	$189.40
Purchase #7	$18.64	10.649%	$20.625	$20.63	$20.65	$20.60
7 purchase totals =	$569.25		$614.8919	$614.89	$614.90	$614.90