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	$123.33	11.708%	$137.7695	$137.77	$137.75	$137.80
Purchase #2	$121.46	5.261%	$127.85	$127.85	$127.85	$127.90
Purchase #3	$154.45	4.109%	$160.7964	$160.80	$160.80	$160.80
Purchase #4	$86.79	11.598%	$96.8559	$96.86	$96.85	$96.90
Purchase #5	$12.40	5.808%	$13.1202	$13.12	$13.10	$13.10
Purchase #6	$148.72	13.466%	$168.7466	$168.75	$168.75	$168.70
Purchase #7	$225.72	12.178%	$253.2082	$253.21	$253.20	$253.20
7 purchase totals =	$872.87		$958.3468	$958.36	$958.30	$958.40