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	$62.88	11.480%	$70.0986	$70.10	$70.10	$70.10
Purchase #2	$69.33	4.814%	$72.6675	$72.67	$72.65	$72.70
Purchase #3	$93.59	12.578%	$105.3618	$105.36	$105.35	$105.40
Purchase #4	$52.27	7.548%	$56.2153	$56.22	$56.20	$56.20
Purchase #5	$67.37	7.519%	$72.4356	$72.44	$72.45	$72.40
Purchase #6	$80.58	12.223%	$90.4293	$90.43	$90.45	$90.40
Purchase #7	$59.79	5.531%	$63.097	$63.10	$63.10	$63.10
7 purchase totals =	$485.81		$530.3051	$530.32	$530.30	$530.30