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	$32.88	12.845%	$37.1034	$37.10	$37.10	$37.10
Purchase #2	$160.72	6.510%	$171.1829	$171.18	$171.20	$171.20
Purchase #3	$144.61	12.486%	$162.666	$162.67	$162.65	$162.70
Purchase #4	$242.59	7.429%	$260.612	$260.61	$260.60	$260.60
Purchase #5	$211.83	13.872%	$241.2151	$241.22	$241.20	$241.20
Purchase #6	$25.65	7.235%	$27.5058	$27.51	$27.50	$27.50
Purchase #7	$100.31	3.299%	$103.6192	$103.62	$103.60	$103.60
7 purchase totals =	$918.59		$1,003.9044	$1,003.91	$1,003.85	$1,003.90