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	$83.86	7.673%	$90.2946	$90.29	$90.30	$90.30
Purchase #2	$225.85	13.857%	$257.146	$257.15	$257.15	$257.10
Purchase #3	$198.43	3.173%	$204.7262	$204.73	$204.75	$204.70
Purchase #4	$41.94	11.290%	$46.675	$46.68	$46.70	$46.70
Purchase #5	$176.47	5.139%	$185.5388	$185.54	$185.55	$185.50
Purchase #6	$189.48	4.279%	$197.5878	$197.59	$197.60	$197.60
Purchase #7	$34.80	7.607%	$37.4472	$37.45	$37.45	$37.40
7 purchase totals =	$950.83		$1,019.4156	$1,019.43	$1,019.50	$1,019.30