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	$72.47	8.398%	$78.556	$78.56	$78.55	$78.60
Purchase #2	$40.43	6.612%	$43.1032	$43.10	$43.10	$43.10
Purchase #3	$112.69	7.598%	$121.2522	$121.25	$121.25	$121.30
Purchase #4	$111.99	5.414%	$118.0531	$118.05	$118.05	$118.10
Purchase #5	$82.29	7.555%	$88.507	$88.51	$88.50	$88.50
Purchase #6	$83.74	10.867%	$92.84	$92.84	$92.85	$92.80
Purchase #7	$132.86	10.672%	$147.0388	$147.04	$147.05	$147.00
7 purchase totals =	$636.47		$689.3503	$689.35	$689.35	$689.40