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	$136.62	13.718%	$155.3615	$155.36	$155.35	$155.40
Purchase #2	$19.69	4.683%	$20.6121	$20.61	$20.60	$20.60
Purchase #3	$163.59	10.377%	$180.5657	$180.57	$180.55	$180.60
Purchase #4	$224.87	6.243%	$238.9086	$238.91	$238.90	$238.90
Purchase #5	$233.69	7.230%	$250.5858	$250.59	$250.60	$250.60
Purchase #6	$188.50	6.404%	$200.5715	$200.57	$200.55	$200.60
Purchase #7	$150.63	8.774%	$163.8463	$163.85	$163.85	$163.80
7 purchase totals =	$1,117.59		$1,210.4515	$1,210.46	$1,210.40	$1,210.50