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	$90.36	13.417%	$102.4836	$102.48	$102.50	$102.50
Purchase #2	$105.64	7.756%	$113.8334	$113.83	$113.85	$113.80
Purchase #3	$250.25	3.651%	$259.3866	$259.39	$259.40	$259.40
Purchase #4	$214.76	5.779%	$227.171	$227.17	$227.15	$227.20
Purchase #5	$67.82	13.768%	$77.1575	$77.16	$77.15	$77.20
Purchase #6	$179.42	9.298%	$196.1025	$196.10	$196.10	$196.10
Purchase #7	$5.60	10.339%	$6.179	$6.18	$6.20	$6.20
7 purchase totals =	$913.85		$982.3136	$982.31	$982.35	$982.40