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	$84.90	6.188%	$90.1536	$90.15	$90.15	$90.20
Purchase #2	$35.34	8.638%	$38.3927	$38.39	$38.40	$38.40
Purchase #3	$205.27	5.236%	$216.0179	$216.02	$216.00	$216.00
Purchase #4	$6.53	9.585%	$7.1559	$7.16	$7.15	$7.20
Purchase #5	$166.34	9.270%	$181.7597	$181.76	$181.75	$181.80
Purchase #6	$225.57	8.137%	$243.9246	$243.92	$243.90	$243.90
Purchase #7	$247.81	3.433%	$256.3173	$256.32	$256.30	$256.30
7 purchase totals =	$971.76		$1,033.7217	$1,033.72	$1,033.65	$1,033.80