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	$49.67	7.574%	$53.432	$53.43	$53.45	$53.40
Purchase #2	$100.67	8.610%	$109.3377	$109.34	$109.35	$109.30
Purchase #3	$173.74	8.774%	$188.9839	$188.98	$189.00	$189.00
Purchase #4	$116.70	9.111%	$127.3325	$127.33	$127.35	$127.30
Purchase #5	$108.69	4.621%	$113.7126	$113.71	$113.70	$113.70
Purchase #6	$184.47	6.555%	$196.562	$196.56	$196.55	$196.60
Purchase #7	$187.31	6.410%	$199.3166	$199.32	$199.30	$199.30
7 purchase totals =	$921.25		$988.6773	$988.67	$988.70	$988.60