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	$226.30	10.827%	$250.8015	$250.80	$250.80	$250.80
Purchase #2	$178.62	7.743%	$192.4505	$192.45	$192.45	$192.50
Purchase #3	$229.82	6.151%	$243.9562	$243.96	$243.95	$244.00
Purchase #4	$58.86	5.143%	$61.8872	$61.89	$61.90	$61.90
Purchase #5	$57.56	11.779%	$64.34	$64.34	$64.35	$64.30
Purchase #6	$75.94	13.143%	$85.9208	$85.92	$85.90	$85.90
Purchase #7	$51.37	12.695%	$57.8914	$57.89	$57.90	$57.90
7 purchase totals =	$878.47		$957.2476	$957.25	$957.25	$957.30