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	$56.77	4.543%	$59.3491	$59.35	$59.35	$59.30
Purchase #2	$18.40	3.289%	$19.0052	$19.01	$19.00	$19.00
Purchase #3	$212.77	9.794%	$233.6087	$233.61	$233.60	$233.60
Purchase #4	$52.29	13.604%	$59.4035	$59.40	$59.40	$59.40
Purchase #5	$6.98	3.120%	$7.1978	$7.20	$7.20	$7.20
Purchase #6	$220.26	4.807%	$230.8479	$230.85	$230.85	$230.80
Purchase #7	$235.49	5.577%	$248.6233	$248.62	$248.60	$248.60
7 purchase totals =	$802.96		$858.0355	$858.04	$858.00	$857.90