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	$191.49	11.568%	$213.6416	$213.64	$213.65	$213.60
Purchase #2	$238.46	4.480%	$249.143	$249.14	$249.15	$249.10
Purchase #3	$123.73	10.378%	$136.5707	$136.57	$136.55	$136.60
Purchase #4	$219.72	9.634%	$240.8878	$240.89	$240.90	$240.90
Purchase #5	$39.80	6.658%	$42.4499	$42.45	$42.45	$42.40
Purchase #6	$178.71	3.343%	$184.6843	$184.68	$184.70	$184.70
Purchase #7	$11.94	12.277%	$13.4059	$13.41	$13.40	$13.40
7 purchase totals =	$1,003.85		$1,080.7832	$1,080.78	$1,080.80	$1,080.70