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	$85.31	5.648%	$90.1283	$90.13	$90.15	$90.10
Purchase #2	$90.85	9.162%	$99.1737	$99.17	$99.15	$99.20
Purchase #3	$65.72	6.734%	$70.1456	$70.15	$70.15	$70.10
Purchase #4	$226.36	5.750%	$239.3757	$239.38	$239.40	$239.40
Purchase #5	$179.69	12.532%	$202.2088	$202.21	$202.20	$202.20
Purchase #6	$79.39	8.817%	$86.3898	$86.39	$86.40	$86.40
Purchase #7	$112.33	13.717%	$127.7383	$127.74	$127.75	$127.70
7 purchase totals =	$839.65		$915.1602	$915.17	$915.20	$915.10