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	$96.74	3.116%	$99.7544	$99.75	$99.75	$99.80
Purchase #2	$42.34	5.121%	$44.5082	$44.51	$44.50	$44.50
Purchase #3	$35.52	5.502%	$37.4743	$37.47	$37.45	$37.50
Purchase #4	$239.60	3.759%	$248.6066	$248.61	$248.60	$248.60
Purchase #5	$84.67	5.775%	$89.5597	$89.56	$89.55	$89.60
Purchase #6	$50.85	4.469%	$53.1225	$53.12	$53.10	$53.10
Purchase #7	$194.37	3.382%	$200.9436	$200.94	$200.95	$200.90
7 purchase totals =	$744.09		$773.9693	$773.96	$773.90	$774.00