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	$124.64	3.300%	$128.7531	$128.75	$128.75	$128.80
Purchase #2	$95.96	10.154%	$105.7038	$105.70	$105.70	$105.70
Purchase #3	$72.73	9.202%	$79.4226	$79.42	$79.40	$79.40
Purchase #4	$144.61	4.636%	$151.3141	$151.31	$151.30	$151.30
Purchase #5	$47.75	12.189%	$53.5702	$53.57	$53.55	$53.60
Purchase #6	$10.50	7.426%	$11.2797	$11.28	$11.30	$11.30
Purchase #7	$6.59	12.244%	$7.3969	$7.40	$7.40	$7.40
7 purchase totals =	$502.78		$537.4404	$537.43	$537.40	$537.50