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	$177.92	5.172%	$187.122	$187.12	$187.10	$187.10
Purchase #2	$90.85	7.333%	$97.512	$97.51	$97.50	$97.50
Purchase #3	$72.86	13.251%	$82.5147	$82.51	$82.50	$82.50
Purchase #4	$219.33	8.705%	$238.4227	$238.42	$238.40	$238.40
Purchase #5	$49.25	11.330%	$54.83	$54.83	$54.85	$54.80
Purchase #6	$143.73	11.872%	$160.7936	$160.79	$160.80	$160.80
Purchase #7	$147.65	8.347%	$159.9743	$159.97	$159.95	$160.00
7 purchase totals =	$901.59		$981.1693	$981.15	$981.10	$981.10