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	$20.97	7.439%	$22.53	$22.53	$22.55	$22.50
Purchase #2	$168.93	12.364%	$189.8165	$189.82	$189.80	$189.80
Purchase #3	$38.29	9.681%	$41.9969	$42.00	$42.00	$42.00
Purchase #4	$244.78	3.675%	$253.7757	$253.78	$253.80	$253.80
Purchase #5	$250.70	10.231%	$276.3491	$276.35	$276.35	$276.30
Purchase #6	$56.65	9.250%	$61.8901	$61.89	$61.90	$61.90
Purchase #7	$178.75	11.834%	$199.9033	$199.90	$199.90	$199.90
7 purchase totals =	$959.07		$1,046.2616	$1,046.27	$1,046.30	$1,046.20