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	$34.63	5.340%	$36.4792	$36.48	$36.50	$36.50
Purchase #2	$118.75	10.351%	$131.0418	$131.04	$131.05	$131.00
Purchase #3	$104.55	8.400%	$113.3322	$113.33	$113.35	$113.30
Purchase #4	$85.44	6.864%	$91.3046	$91.30	$91.30	$91.30
Purchase #5	$53.71	11.422%	$59.8448	$59.84	$59.85	$59.80
Purchase #6	$145.35	6.132%	$154.2629	$154.26	$154.25	$154.30
Purchase #7	$46.71	12.589%	$52.5903	$52.59	$52.60	$52.60
7 purchase totals =	$589.14		$638.8558	$638.84	$638.90	$638.80