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	$89.61	10.614%	$99.1212	$99.12	$99.10	$99.10
Purchase #2	$189.96	3.635%	$196.865	$196.87	$196.85	$196.90
Purchase #3	$228.69	5.362%	$240.9524	$240.95	$240.95	$241.00
Purchase #4	$203.36	12.720%	$229.2274	$229.23	$229.25	$229.20
Purchase #5	$124.95	8.778%	$135.9181	$135.92	$135.90	$135.90
Purchase #6	$194.61	11.167%	$216.3421	$216.34	$216.35	$216.30
Purchase #7	$40.28	4.845%	$42.2316	$42.23	$42.25	$42.20
7 purchase totals =	$1,071.46		$1,160.6578	$1,160.66	$1,160.65	$1,160.60