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	$179.46	5.771%	$189.8166	$189.82	$189.80	$189.80
Purchase #2	$58.60	10.736%	$64.8913	$64.89	$64.90	$64.90
Purchase #3	$194.77	12.217%	$218.5651	$218.57	$218.55	$218.60
Purchase #4	$134.82	12.856%	$152.1525	$152.15	$152.15	$152.20
Purchase #5	$160.67	13.220%	$181.9106	$181.91	$181.90	$181.90
Purchase #6	$71.83	13.833%	$81.7662	$81.77	$81.75	$81.80
Purchase #7	$95.66	7.263%	$102.6078	$102.61	$102.60	$102.60
7 purchase totals =	$895.81		$991.7101	$991.72	$991.65	$991.80