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	$178.41	10.223%	$196.6489	$196.65	$196.65	$196.60
Purchase #2	$66.85	5.181%	$70.3135	$70.31	$70.30	$70.30
Purchase #3	$40.48	13.155%	$45.8051	$45.81	$45.80	$45.80
Purchase #4	$175.75	7.483%	$188.9014	$188.90	$188.90	$188.90
Purchase #5	$22.48	6.158%	$23.8643	$23.86	$23.85	$23.90
Purchase #6	$18.97	9.851%	$20.8387	$20.84	$20.85	$20.80
Purchase #7	$18.48	13.428%	$20.9615	$20.96	$20.95	$21.00
7 purchase totals =	$521.42		$567.3334	$567.33	$567.30	$567.30