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	$45.90	5.700%	$48.5163	$48.52	$48.50	$48.50
Purchase #2	$238.56	12.260%	$267.8075	$267.81	$267.80	$267.80
Purchase #3	$94.55	4.819%	$99.1064	$99.11	$99.10	$99.10
Purchase #4	$50.71	6.272%	$53.8905	$53.89	$53.90	$53.90
Purchase #5	$165.39	5.441%	$174.3889	$174.39	$174.40	$174.40
Purchase #6	$210.78	10.607%	$233.1374	$233.14	$233.15	$233.10
Purchase #7	$74.33	5.756%	$78.6084	$78.61	$78.60	$78.60
7 purchase totals =	$880.22		$955.4554	$955.47	$955.45	$955.40