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	$50.27	4.489%	$52.5266	$52.53	$52.55	$52.50
Purchase #2	$103.42	4.592%	$108.169	$108.17	$108.15	$108.20
Purchase #3	$86.56	4.306%	$90.2873	$90.29	$90.30	$90.30
Purchase #4	$66.65	5.289%	$70.1751	$70.18	$70.20	$70.20
Purchase #5	$120.31	11.681%	$134.3634	$134.36	$134.35	$134.40
Purchase #6	$132.56	5.707%	$140.1252	$140.13	$140.15	$140.10
Purchase #7	$39.95	3.364%	$41.2939	$41.29	$41.30	$41.30
7 purchase totals =	$599.72		$636.9405	$636.95	$637.00	$637.00