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	$84.49	4.759%	$88.5109	$88.51	$88.50	$88.50
Purchase #2	$37.97	6.444%	$40.4168	$40.42	$40.40	$40.40
Purchase #3	$217.31	7.575%	$233.7712	$233.77	$233.75	$233.80
Purchase #4	$224.42	10.607%	$248.2242	$248.22	$248.20	$248.20
Purchase #5	$169.59	9.337%	$185.4246	$185.42	$185.40	$185.40
Purchase #6	$219.34	9.443%	$240.0523	$240.05	$240.05	$240.10
Purchase #7	$35.78	12.802%	$40.3606	$40.36	$40.35	$40.40
7 purchase totals =	$988.90		$1,076.7606	$1,076.75	$1,076.65	$1,076.80