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	$81.82	6.494%	$87.1334	$87.13	$87.15	$87.10
Purchase #2	$249.83	12.454%	$280.9438	$280.94	$280.95	$280.90
Purchase #3	$76.78	3.164%	$79.2093	$79.21	$79.20	$79.20
Purchase #4	$233.70	12.741%	$263.4757	$263.48	$263.50	$263.50
Purchase #5	$119.75	10.743%	$132.6147	$132.61	$132.60	$132.60
Purchase #6	$189.83	12.135%	$212.8659	$212.87	$212.85	$212.90
Purchase #7	$80.96	10.818%	$89.7183	$89.72	$89.70	$89.70
7 purchase totals =	$1,032.67		$1,145.9611	$1,145.96	$1,145.95	$1,145.90