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	$53.69	9.262%	$58.6628	$58.66	$58.65	$58.70
Purchase #2	$79.70	7.309%	$85.5253	$85.53	$85.55	$85.50
Purchase #3	$188.64	4.273%	$196.7006	$196.70	$196.70	$196.70
Purchase #4	$140.46	13.546%	$159.4867	$159.49	$159.50	$159.50
Purchase #5	$86.83	6.439%	$92.421	$92.42	$92.40	$92.40
Purchase #6	$173.75	9.438%	$190.1485	$190.15	$190.15	$190.10
Purchase #7	$76.29	3.339%	$78.8373	$78.84	$78.85	$78.80
7 purchase totals =	$799.36		$861.7822	$861.79	$861.80	$861.70