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	$233.30	13.168%	$264.0209	$264.02	$264.00	$264.00
Purchase #2	$92.74	12.373%	$104.2147	$104.21	$104.20	$104.20
Purchase #3	$166.37	4.831%	$174.4073	$174.41	$174.40	$174.40
Purchase #4	$86.35	5.229%	$90.8652	$90.87	$90.85	$90.90
Purchase #5	$178.45	6.279%	$189.6549	$189.65	$189.65	$189.70
Purchase #6	$59.74	9.551%	$65.4458	$65.45	$65.45	$65.40
Purchase #7	$100.74	11.274%	$112.0974	$112.10	$112.10	$112.10
7 purchase totals =	$917.69		$1,000.7062	$1,000.71	$1,000.65	$1,000.70