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	$98.30	12.674%	$110.7585	$110.76	$110.75	$110.80
Purchase #2	$231.53	3.131%	$238.7792	$238.78	$238.80	$238.80
Purchase #3	$134.56	10.442%	$148.6108	$148.61	$148.60	$148.60
Purchase #4	$125.58	4.637%	$131.4031	$131.40	$131.40	$131.40
Purchase #5	$95.50	10.143%	$105.1866	$105.19	$105.20	$105.20
Purchase #6	$19.62	7.809%	$21.1521	$21.15	$21.15	$21.20
Purchase #7	$25.93	9.572%	$28.412	$28.41	$28.40	$28.40
7 purchase totals =	$731.02		$784.3023	$784.30	$784.30	$784.40