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	$97.28	9.133%	$106.1646	$106.16	$106.15	$106.20
Purchase #2	$86.96	3.772%	$90.2401	$90.24	$90.25	$90.20
Purchase #3	$147.96	12.532%	$166.5023	$166.50	$166.50	$166.50
Purchase #4	$82.53	11.343%	$91.8914	$91.89	$91.90	$91.90
Purchase #5	$229.98	10.444%	$253.9991	$254.00	$254.00	$254.00
Purchase #6	$85.88	10.705%	$95.0735	$95.07	$95.05	$95.10
Purchase #7	$76.59	12.112%	$85.8666	$85.87	$85.85	$85.90
7 purchase totals =	$807.18		$889.7376	$889.73	$889.70	$889.80