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	$37.91	11.824%	$42.3925	$42.39	$42.40	$42.40
Purchase #2	$32.46	3.615%	$33.6334	$33.63	$33.65	$33.60
Purchase #3	$101.68	7.709%	$109.5185	$109.52	$109.50	$109.50
Purchase #4	$58.76	13.441%	$66.6579	$66.66	$66.65	$66.70
Purchase #5	$138.41	5.702%	$146.3021	$146.30	$146.30	$146.30
Purchase #6	$50.67	12.369%	$56.9374	$56.94	$56.95	$56.90
Purchase #7	$236.96	5.384%	$249.7179	$249.72	$249.70	$249.70
7 purchase totals =	$656.85		$705.1597	$705.16	$705.15	$705.10