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	$26.39	5.304%	$27.7897	$27.79	$27.80	$27.80
Purchase #2	$152.75	9.623%	$167.4491	$167.45	$167.45	$167.40
Purchase #3	$9.82	7.143%	$10.5214	$10.52	$10.50	$10.50
Purchase #4	$85.96	8.546%	$93.3061	$93.31	$93.30	$93.30
Purchase #5	$151.41	9.320%	$165.5214	$165.52	$165.50	$165.50
Purchase #6	$32.61	11.165%	$36.2509	$36.25	$36.25	$36.30
Purchase #7	$142.35	8.170%	$153.98	$153.98	$154.00	$154.00
7 purchase totals =	$601.29		$654.8186	$654.82	$654.80	$654.80