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	$93.67	10.445%	$103.4538	$103.45	$103.45	$103.50
Purchase #2	$55.47	6.625%	$59.1449	$59.14	$59.15	$59.10
Purchase #3	$106.53	9.874%	$117.0488	$117.05	$117.05	$117.00
Purchase #4	$135.45	4.625%	$141.7146	$141.71	$141.70	$141.70
Purchase #5	$205.78	3.612%	$213.2128	$213.21	$213.20	$213.20
Purchase #6	$179.75	10.444%	$198.5231	$198.52	$198.50	$198.50
Purchase #7	$53.32	7.763%	$57.4592	$57.46	$57.45	$57.50
7 purchase totals =	$829.97		$890.5572	$890.54	$890.50	$890.50