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	$155.31	3.564%	$160.8452	$160.85	$160.85	$160.80
Purchase #2	$197.86	10.841%	$219.31	$219.31	$219.30	$219.30
Purchase #3	$13.86	11.301%	$15.4263	$15.43	$15.45	$15.40
Purchase #4	$136.26	12.437%	$153.2067	$153.21	$153.20	$153.20
Purchase #5	$227.46	11.818%	$254.3412	$254.34	$254.35	$254.30
Purchase #6	$98.45	13.143%	$111.3893	$111.39	$111.40	$111.40
Purchase #7	$218.36	10.518%	$241.3271	$241.33	$241.35	$241.30
7 purchase totals =	$1,047.56		$1,155.8458	$1,155.86	$1,155.90	$1,155.70