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	$172.73	9.185%	$188.5953	$188.60	$188.60	$188.60
Purchase #2	$249.28	9.536%	$273.0513	$273.05	$273.05	$273.10
Purchase #3	$43.30	3.562%	$44.8423	$44.84	$44.85	$44.80
Purchase #4	$174.53	12.558%	$196.4475	$196.45	$196.45	$196.40
Purchase #5	$22.43	8.792%	$24.402	$24.40	$24.40	$24.40
Purchase #6	$77.66	5.708%	$82.0928	$82.09	$82.10	$82.10
Purchase #7	$77.25	6.770%	$82.4798	$82.48	$82.50	$82.50
7 purchase totals =	$817.18		$891.9110	$891.91	$891.95	$891.90