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	$99.38	9.859%	$109.1779	$109.18	$109.20	$109.20
Purchase #2	$77.89	10.662%	$86.1946	$86.19	$86.20	$86.20
Purchase #3	$53.27	7.425%	$57.2253	$57.23	$57.25	$57.20
Purchase #4	$58.84	9.315%	$64.3209	$64.32	$64.30	$64.30
Purchase #5	$77.39	13.178%	$87.5885	$87.59	$87.60	$87.60
Purchase #6	$132.61	6.814%	$141.646	$141.65	$141.65	$141.60
Purchase #7	$124.53	5.416%	$131.2745	$131.27	$131.25	$131.30
7 purchase totals =	$623.91		$677.4277	$677.43	$677.45	$677.40