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	$53.34	8.654%	$57.956	$57.96	$57.95	$58.00
Purchase #2	$137.68	12.462%	$154.8377	$154.84	$154.85	$154.80
Purchase #3	$139.68	10.574%	$154.4498	$154.45	$154.45	$154.40
Purchase #4	$33.28	9.291%	$36.372	$36.37	$36.35	$36.40
Purchase #5	$189.72	3.761%	$196.8554	$196.86	$196.85	$196.90
Purchase #6	$32.59	10.231%	$35.9243	$35.92	$35.90	$35.90
Purchase #7	$33.87	9.533%	$37.0988	$37.10	$37.10	$37.10
7 purchase totals =	$620.16		$673.4940	$673.50	$673.45	$673.50