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	$243.26	6.856%	$259.9379	$259.94	$259.95	$259.90
Purchase #2	$162.79	10.516%	$179.909	$179.91	$179.90	$179.90
Purchase #3	$53.74	10.491%	$59.3779	$59.38	$59.40	$59.40
Purchase #4	$196.50	12.549%	$221.1588	$221.16	$221.15	$221.20
Purchase #5	$12.34	10.799%	$13.6726	$13.67	$13.65	$13.70
Purchase #6	$98.78	5.124%	$103.8415	$103.84	$103.85	$103.80
Purchase #7	$68.52	12.710%	$77.2289	$77.23	$77.25	$77.20
7 purchase totals =	$835.93		$915.1266	$915.13	$915.15	$915.10