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	$37.47	7.771%	$40.3818	$40.38	$40.40	$40.40
Purchase #2	$84.48	6.289%	$89.7929	$89.79	$89.80	$89.80
Purchase #3	$244.61	7.725%	$263.5061	$263.51	$263.50	$263.50
Purchase #4	$225.65	7.107%	$241.6869	$241.69	$241.70	$241.70
Purchase #5	$120.46	12.541%	$135.5669	$135.57	$135.55	$135.60
Purchase #6	$139.38	6.290%	$148.147	$148.15	$148.15	$148.10
Purchase #7	$75.64	3.406%	$78.2163	$78.22	$78.20	$78.20
7 purchase totals =	$927.69		$997.2979	$997.31	$997.30	$997.30