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	$29.80	11.271%	$33.1588	$33.16	$33.15	$33.20
Purchase #2	$98.52	13.121%	$111.4468	$111.45	$111.45	$111.40
Purchase #3	$129.65	9.171%	$141.5402	$141.54	$141.55	$141.50
Purchase #4	$51.76	9.279%	$56.5628	$56.56	$56.55	$56.60
Purchase #5	$206.54	9.259%	$225.6635	$225.66	$225.65	$225.70
Purchase #6	$191.87	12.124%	$215.1323	$215.13	$215.15	$215.10
Purchase #7	$96.94	9.739%	$106.381	$106.38	$106.40	$106.40
7 purchase totals =	$805.08		$889.8854	$889.88	$889.90	$889.90