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	$93.48	12.824%	$105.4679	$105.47	$105.45	$105.50
Purchase #2	$57.53	6.664%	$61.3638	$61.36	$61.35	$61.40
Purchase #3	$89.88	12.405%	$101.0296	$101.03	$101.05	$101.00
Purchase #4	$104.52	9.347%	$114.2895	$114.29	$114.30	$114.30
Purchase #5	$73.64	9.408%	$80.5681	$80.57	$80.55	$80.60
Purchase #6	$168.38	4.759%	$176.3932	$176.39	$176.40	$176.40
Purchase #7	$134.27	11.803%	$150.1179	$150.12	$150.10	$150.10
7 purchase totals =	$721.70		$789.2300	$789.23	$789.20	$789.30