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	$222.85	12.303%	$250.2672	$250.27	$250.25	$250.30
Purchase #2	$226.56	3.666%	$234.8657	$234.87	$234.85	$234.90
Purchase #3	$67.68	3.595%	$70.1131	$70.11	$70.10	$70.10
Purchase #4	$175.78	10.555%	$194.3336	$194.33	$194.35	$194.30
Purchase #5	$203.69	3.531%	$210.8823	$210.88	$210.90	$210.90
Purchase #6	$122.64	13.805%	$139.5705	$139.57	$139.55	$139.60
Purchase #7	$59.77	12.225%	$67.0769	$67.08	$67.10	$67.10
7 purchase totals =	$1,078.97		$1,167.1093	$1,167.11	$1,167.10	$1,167.20