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	$137.26	13.351%	$155.5856	$155.59	$155.60	$155.60
Purchase #2	$240.76	13.205%	$272.5524	$272.55	$272.55	$272.60
Purchase #3	$250.59	7.303%	$268.8906	$268.89	$268.90	$268.90
Purchase #4	$237.71	11.736%	$265.6076	$265.61	$265.60	$265.60
Purchase #5	$246.78	7.135%	$264.3878	$264.39	$264.40	$264.40
Purchase #6	$146.47	6.681%	$156.2557	$156.26	$156.25	$156.30
Purchase #7	$232.61	13.282%	$263.5053	$263.51	$263.50	$263.50
7 purchase totals =	$1,492.18		$1,646.7850	$1,646.80	$1,646.80	$1,646.90