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	$97.65	6.837%	$104.3263	$104.33	$104.35	$104.30
Purchase #2	$33.52	11.737%	$37.4542	$37.45	$37.45	$37.50
Purchase #3	$80.76	11.631%	$90.1532	$90.15	$90.15	$90.20
Purchase #4	$128.61	5.235%	$135.3427	$135.34	$135.35	$135.30
Purchase #5	$7.26	8.171%	$7.8532	$7.85	$7.85	$7.90
Purchase #6	$161.65	4.664%	$169.1894	$169.19	$169.20	$169.20
Purchase #7	$166.86	11.435%	$185.9404	$185.94	$185.95	$185.90
7 purchase totals =	$676.31		$730.2594	$730.25	$730.30	$730.30