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	$116.99	10.128%	$128.8387	$128.84	$128.85	$128.80
Purchase #2	$175.95	5.345%	$185.3545	$185.35	$185.35	$185.40
Purchase #3	$81.42	5.317%	$85.7491	$85.75	$85.75	$85.70
Purchase #4	$55.89	9.657%	$61.2873	$61.29	$61.30	$61.30
Purchase #5	$55.99	5.429%	$59.0297	$59.03	$59.05	$59.00
Purchase #6	$186.79	9.124%	$203.8327	$203.83	$203.85	$203.80
Purchase #7	$100.35	13.662%	$114.0598	$114.06	$114.05	$114.10
7 purchase totals =	$773.38		$838.1518	$838.15	$838.20	$838.10