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	$44.57	4.311%	$46.4914	$46.49	$46.50	$46.50
Purchase #2	$54.29	9.841%	$59.6327	$59.63	$59.65	$59.60
Purchase #3	$100.35	9.455%	$109.8381	$109.84	$109.85	$109.80
Purchase #4	$7.62	11.262%	$8.4782	$8.48	$8.50	$8.50
Purchase #5	$229.73	4.678%	$240.4768	$240.48	$240.50	$240.50
Purchase #6	$78.69	10.503%	$86.9548	$86.95	$86.95	$87.00
Purchase #7	$96.65	5.843%	$102.2973	$102.30	$102.30	$102.30
7 purchase totals =	$611.90		$654.1693	$654.17	$654.25	$654.20