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	$227.27	11.396%	$253.1697	$253.17	$253.15	$253.20
Purchase #2	$109.56	13.355%	$124.1917	$124.19	$124.20	$124.20
Purchase #3	$35.60	11.393%	$39.6559	$39.66	$39.65	$39.70
Purchase #4	$57.34	3.597%	$59.4025	$59.40	$59.40	$59.40
Purchase #5	$104.85	4.235%	$109.2904	$109.29	$109.30	$109.30
Purchase #6	$96.58	9.611%	$105.8623	$105.86	$105.85	$105.90
Purchase #7	$123.98	4.678%	$129.7798	$129.78	$129.80	$129.80
7 purchase totals =	$755.18		$821.3523	$821.35	$821.35	$821.50