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	$38.75	9.637%	$42.4843	$42.48	$42.50	$42.50
Purchase #2	$230.38	4.611%	$241.0028	$241.00	$241.00	$241.00
Purchase #3	$70.45	10.862%	$78.1023	$78.10	$78.10	$78.10
Purchase #4	$25.80	6.191%	$27.3973	$27.40	$27.40	$27.40
Purchase #5	$217.90	10.241%	$240.2151	$240.22	$240.20	$240.20
Purchase #6	$79.32	12.277%	$89.0581	$89.06	$89.05	$89.10
Purchase #7	$8.91	10.454%	$9.8415	$9.84	$9.85	$9.80
7 purchase totals =	$671.51		$728.1014	$728.10	$728.10	$728.10