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	$98.56	7.291%	$105.746	$105.75	$105.75	$105.70
Purchase #2	$193.61	6.693%	$206.5683	$206.57	$206.55	$206.60
Purchase #3	$83.99	5.636%	$88.7237	$88.72	$88.70	$88.70
Purchase #4	$109.98	3.229%	$113.5313	$113.53	$113.55	$113.50
Purchase #5	$249.91	4.753%	$261.7882	$261.79	$261.80	$261.80
Purchase #6	$62.39	7.786%	$67.2477	$67.25	$67.25	$67.20
Purchase #7	$250.93	11.390%	$279.5109	$279.51	$279.50	$279.50
7 purchase totals =	$1,049.37		$1,123.1161	$1,123.12	$1,123.10	$1,123.00