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	$28.68	7.139%	$30.7275	$30.73	$30.75	$30.70
Purchase #2	$86.32	3.659%	$89.4784	$89.48	$89.50	$89.50
Purchase #3	$57.55	6.774%	$61.4484	$61.45	$61.45	$61.40
Purchase #4	$52.43	7.318%	$56.2668	$56.27	$56.25	$56.30
Purchase #5	$93.38	8.713%	$101.5162	$101.52	$101.50	$101.50
Purchase #6	$128.39	4.485%	$134.1483	$134.15	$134.15	$134.10
Purchase #7	$89.47	13.681%	$101.7104	$101.71	$101.70	$101.70
7 purchase totals =	$536.22		$575.2960	$575.31	$575.30	$575.20