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	$103.33	12.223%	$115.96	$115.96	$115.95	$116.00
Purchase #2	$204.41	9.538%	$223.9066	$223.91	$223.90	$223.90
Purchase #3	$68.28	6.782%	$72.9107	$72.91	$72.90	$72.90
Purchase #4	$199.67	13.818%	$227.2604	$227.26	$227.25	$227.30
Purchase #5	$179.38	6.259%	$190.6074	$190.61	$190.60	$190.60
Purchase #6	$206.41	4.455%	$215.6056	$215.61	$215.60	$215.60
Purchase #7	$247.78	11.475%	$276.2128	$276.21	$276.20	$276.20
7 purchase totals =	$1,209.26		$1,322.4635	$1,322.47	$1,322.40	$1,322.50