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	$169.60	9.644%	$185.9562	$185.96	$185.95	$186.00
Purchase #2	$149.67	9.717%	$164.2134	$164.21	$164.20	$164.20
Purchase #3	$47.32	6.832%	$50.5529	$50.55	$50.55	$50.60
Purchase #4	$96.90	12.792%	$109.2954	$109.30	$109.30	$109.30
Purchase #5	$61.46	3.290%	$63.482	$63.48	$63.50	$63.50
Purchase #6	$192.71	6.486%	$205.2092	$205.21	$205.20	$205.20
Purchase #7	$210.82	6.401%	$224.3146	$224.31	$224.30	$224.30
7 purchase totals =	$928.48		$1,003.0237	$1,003.02	$1,003.00	$1,003.10