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	$115.97	3.874%	$120.4627	$120.46	$120.45	$120.50
Purchase #2	$54.74	9.526%	$59.9545	$59.95	$59.95	$60.00
Purchase #3	$56.52	9.578%	$61.9335	$61.93	$61.95	$61.90
Purchase #4	$180.38	6.404%	$191.9315	$191.93	$191.95	$191.90
Purchase #5	$30.97	6.428%	$32.9608	$32.96	$32.95	$33.00
Purchase #6	$198.34	9.838%	$217.8527	$217.85	$217.85	$217.90
Purchase #7	$139.76	10.298%	$154.1525	$154.15	$154.15	$154.20
7 purchase totals =	$776.68		$839.2482	$839.23	$839.25	$839.40