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	$118.35	10.314%	$130.5566	$130.56	$130.55	$130.60
Purchase #2	$103.88	9.772%	$114.0312	$114.03	$114.05	$114.00
Purchase #3	$108.33	11.292%	$120.5626	$120.56	$120.55	$120.60
Purchase #4	$70.28	10.593%	$77.7248	$77.72	$77.70	$77.70
Purchase #5	$250.53	6.774%	$267.5009	$267.50	$267.50	$267.50
Purchase #6	$89.77	10.662%	$99.3413	$99.34	$99.35	$99.30
Purchase #7	$25.87	5.679%	$27.3392	$27.34	$27.35	$27.30
7 purchase totals =	$767.01		$837.0566	$837.05	$837.05	$837.00