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	$70.50	12.499%	$79.3118	$79.31	$79.30	$79.30
Purchase #2	$37.30	11.649%	$41.6451	$41.65	$41.65	$41.60
Purchase #3	$80.61	9.504%	$88.2712	$88.27	$88.25	$88.30
Purchase #4	$182.46	9.656%	$200.0783	$200.08	$200.10	$200.10
Purchase #5	$39.25	12.472%	$44.1453	$44.15	$44.15	$44.10
Purchase #6	$6.45	11.353%	$7.1823	$7.18	$7.20	$7.20
Purchase #7	$91.48	9.788%	$100.4341	$100.43	$100.45	$100.40
7 purchase totals =	$508.05		$561.0681	$561.07	$561.10	$561.00