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	$45.36	13.624%	$51.5398	$51.54	$51.55	$51.50
Purchase #2	$209.77	4.619%	$219.4593	$219.46	$219.45	$219.50
Purchase #3	$51.69	11.245%	$57.5025	$57.50	$57.50	$57.50
Purchase #4	$179.39	4.865%	$188.1173	$188.12	$188.10	$188.10
Purchase #5	$178.57	6.412%	$190.0199	$190.02	$190.00	$190.00
Purchase #6	$102.46	4.814%	$107.3924	$107.39	$107.40	$107.40
Purchase #7	$162.61	6.547%	$173.2561	$173.26	$173.25	$173.30
7 purchase totals =	$929.85		$987.2873	$987.29	$987.25	$987.30