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	$18.67	4.754%	$19.5576	$19.56	$19.55	$19.60
Purchase #2	$165.47	9.632%	$181.4081	$181.41	$181.40	$181.40
Purchase #3	$246.89	13.313%	$279.7585	$279.76	$279.75	$279.80
Purchase #4	$142.79	8.498%	$154.9243	$154.92	$154.90	$154.90
Purchase #5	$64.61	10.529%	$71.4128	$71.41	$71.40	$71.40
Purchase #6	$45.54	7.333%	$48.8794	$48.88	$48.90	$48.90
Purchase #7	$178.33	4.233%	$185.8787	$185.88	$185.90	$185.90
7 purchase totals =	$862.30		$941.8194	$941.82	$941.80	$941.90