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	$6.71	12.715%	$7.5632	$7.56	$7.55	$7.60
Purchase #2	$101.60	6.386%	$108.0882	$108.09	$108.10	$108.10
Purchase #3	$79.54	8.488%	$86.2914	$86.29	$86.30	$86.30
Purchase #4	$10.25	10.555%	$11.3319	$11.33	$11.35	$11.30
Purchase #5	$181.59	3.194%	$187.39	$187.39	$187.40	$187.40
Purchase #6	$143.78	13.306%	$162.9114	$162.91	$162.90	$162.90
Purchase #7	$232.84	3.276%	$240.4678	$240.47	$240.45	$240.50
7 purchase totals =	$756.31		$804.0439	$804.04	$804.05	$804.10