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	$86.46	4.729%	$90.5487	$90.55	$90.55	$90.50
Purchase #2	$110.78	6.498%	$117.9785	$117.98	$118.00	$118.00
Purchase #3	$147.56	13.654%	$167.7078	$167.71	$167.70	$167.70
Purchase #4	$177.52	8.862%	$193.2518	$193.25	$193.25	$193.30
Purchase #5	$74.93	4.827%	$78.5469	$78.55	$78.55	$78.50
Purchase #6	$17.92	9.453%	$19.614	$19.61	$19.60	$19.60
Purchase #7	$169.84	12.776%	$191.5388	$191.54	$191.55	$191.50
7 purchase totals =	$785.01		$859.1865	$859.19	$859.20	$859.10