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	$80.54	11.393%	$89.7159	$89.72	$89.70	$89.70
Purchase #2	$37.34	3.224%	$38.5438	$38.54	$38.55	$38.50
Purchase #3	$182.41	9.563%	$199.8539	$199.85	$199.85	$199.90
Purchase #4	$224.59	7.650%	$241.7711	$241.77	$241.75	$241.80
Purchase #5	$240.48	11.733%	$268.6955	$268.70	$268.70	$268.70
Purchase #6	$217.37	10.497%	$240.1873	$240.19	$240.20	$240.20
Purchase #7	$40.36	4.403%	$42.1371	$42.14	$42.15	$42.10
7 purchase totals =	$1,023.09		$1,120.9046	$1,120.91	$1,120.90	$1,120.90