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	$189.75	12.107%	$212.723	$212.72	$212.70	$212.70
Purchase #2	$54.45	6.213%	$57.833	$57.83	$57.85	$57.80
Purchase #3	$28.41	5.144%	$29.8714	$29.87	$29.85	$29.90
Purchase #4	$50.66	6.661%	$54.0345	$54.03	$54.05	$54.00
Purchase #5	$37.77	8.347%	$40.9227	$40.92	$40.90	$40.90
Purchase #6	$227.32	10.355%	$250.859	$250.86	$250.85	$250.90
Purchase #7	$170.27	12.439%	$191.4499	$191.45	$191.45	$191.40
7 purchase totals =	$758.63		$837.6935	$837.68	$837.65	$837.60