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	$227.27	13.681%	$258.3628	$258.36	$258.35	$258.40
Purchase #2	$86.61	5.478%	$91.3545	$91.35	$91.35	$91.40
Purchase #3	$250.28	11.513%	$279.0947	$279.09	$279.10	$279.10
Purchase #4	$137.73	3.721%	$142.8549	$142.85	$142.85	$142.90
Purchase #5	$63.67	12.770%	$71.8007	$71.80	$71.80	$71.80
Purchase #6	$165.71	7.288%	$177.7869	$177.79	$177.80	$177.80
Purchase #7	$71.35	8.653%	$77.5239	$77.52	$77.50	$77.50
7 purchase totals =	$1,002.62		$1,098.7784	$1,098.76	$1,098.75	$1,098.90