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	$88.53	13.121%	$100.146	$100.15	$100.15	$100.10
Purchase #2	$94.64	9.865%	$103.9762	$103.98	$104.00	$104.00
Purchase #3	$73.82	11.272%	$82.141	$82.14	$82.15	$82.10
Purchase #4	$97.42	11.541%	$108.6632	$108.66	$108.65	$108.70
Purchase #5	$199.50	9.402%	$218.257	$218.26	$218.25	$218.30
Purchase #6	$18.56	5.750%	$19.6272	$19.63	$19.65	$19.60
Purchase #7	$228.89	12.801%	$258.1902	$258.19	$258.20	$258.20
7 purchase totals =	$801.36		$891.0008	$891.01	$891.05	$891.00