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	$156.96	5.281%	$165.2491	$165.25	$165.25	$165.20
Purchase #2	$72.58	10.389%	$80.1203	$80.12	$80.10	$80.10
Purchase #3	$221.59	10.700%	$245.3001	$245.30	$245.30	$245.30
Purchase #4	$136.60	6.552%	$145.55	$145.55	$145.55	$145.60
Purchase #5	$221.73	3.467%	$229.4174	$229.42	$229.40	$229.40
Purchase #6	$89.45	9.279%	$97.7501	$97.75	$97.75	$97.80
Purchase #7	$59.36	10.376%	$65.5192	$65.52	$65.50	$65.50
7 purchase totals =	$958.27		$1,028.9062	$1,028.91	$1,028.85	$1,028.90