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	$75.57	6.503%	$80.4843	$80.48	$80.50	$80.50
Purchase #2	$191.56	7.349%	$205.6377	$205.64	$205.65	$205.60
Purchase #3	$85.41	11.850%	$95.5311	$95.53	$95.55	$95.50
Purchase #4	$53.54	11.393%	$59.6398	$59.64	$59.65	$59.60
Purchase #5	$201.62	5.575%	$212.8603	$212.86	$212.85	$212.90
Purchase #6	$58.71	12.463%	$66.027	$66.03	$66.05	$66.00
Purchase #7	$130.28	8.357%	$141.1675	$141.17	$141.15	$141.20
7 purchase totals =	$796.69		$861.3477	$861.35	$861.40	$861.30