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	$157.39	7.308%	$168.8921	$168.89	$168.90	$168.90
Purchase #2	$216.83	12.751%	$244.478	$244.48	$244.50	$244.50
Purchase #3	$51.87	8.480%	$56.2686	$56.27	$56.25	$56.30
Purchase #4	$100.48	4.550%	$105.0518	$105.05	$105.05	$105.10
Purchase #5	$219.61	4.319%	$229.095	$229.10	$229.10	$229.10
Purchase #6	$36.35	4.231%	$37.888	$37.89	$37.90	$37.90
Purchase #7	$54.70	4.214%	$57.0051	$57.01	$57.00	$57.00
7 purchase totals =	$837.23		$898.6786	$898.69	$898.70	$898.80