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	$56.71	5.668%	$59.9243	$59.92	$59.90	$59.90
Purchase #2	$207.64	7.849%	$223.9377	$223.94	$223.95	$223.90
Purchase #3	$138.52	10.269%	$152.7446	$152.74	$152.75	$152.70
Purchase #4	$79.38	3.768%	$82.371	$82.37	$82.35	$82.40
Purchase #5	$158.53	3.692%	$164.3829	$164.38	$164.40	$164.40
Purchase #6	$242.59	10.549%	$268.1808	$268.18	$268.20	$268.20
Purchase #7	$188.38	6.580%	$200.7754	$200.78	$200.80	$200.80
7 purchase totals =	$1,071.75		$1,152.3167	$1,152.31	$1,152.35	$1,152.30