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	$45.79	9.507%	$50.1433	$50.14	$50.15	$50.10
Purchase #2	$18.29	6.812%	$19.5359	$19.54	$19.55	$19.50
Purchase #3	$157.86	4.870%	$165.5478	$165.55	$165.55	$165.50
Purchase #4	$191.77	7.504%	$206.1604	$206.16	$206.15	$206.20
Purchase #5	$222.71	5.340%	$234.6027	$234.60	$234.60	$234.60
Purchase #6	$94.44	6.373%	$100.4587	$100.46	$100.45	$100.50
Purchase #7	$204.56	13.631%	$232.4436	$232.44	$232.45	$232.40
7 purchase totals =	$935.42		$1,008.8924	$1,008.89	$1,008.90	$1,008.80