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	$43.83	6.588%	$46.7175	$46.72	$46.70	$46.70
Purchase #2	$55.91	4.498%	$58.4248	$58.42	$58.40	$58.40
Purchase #3	$225.53	3.368%	$233.1259	$233.13	$233.15	$233.10
Purchase #4	$204.46	11.181%	$227.3207	$227.32	$227.30	$227.30
Purchase #5	$72.50	12.142%	$81.303	$81.30	$81.30	$81.30
Purchase #6	$178.72	12.309%	$200.7186	$200.72	$200.70	$200.70
Purchase #7	$139.74	10.331%	$154.1765	$154.18	$154.20	$154.20
7 purchase totals =	$920.69		$1,001.7870	$1,001.79	$1,001.75	$1,001.70