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	$52.63	12.372%	$59.1414	$59.14	$59.15	$59.10
Purchase #2	$25.78	6.621%	$27.4869	$27.49	$27.50	$27.50
Purchase #3	$96.37	3.851%	$100.0812	$100.08	$100.10	$100.10
Purchase #4	$199.87	11.245%	$222.3454	$222.35	$222.35	$222.30
Purchase #5	$135.64	11.422%	$151.1328	$151.13	$151.15	$151.10
Purchase #6	$109.84	6.835%	$117.3476	$117.35	$117.35	$117.30
Purchase #7	$90.53	12.838%	$102.1522	$102.15	$102.15	$102.20
7 purchase totals =	$710.66		$779.6875	$779.69	$779.75	$779.60