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	$56.38	5.328%	$59.3839	$59.38	$59.40	$59.40
Purchase #2	$139.64	7.830%	$150.5738	$150.57	$150.55	$150.60
Purchase #3	$107.36	5.398%	$113.1553	$113.16	$113.15	$113.20
Purchase #4	$98.66	5.599%	$104.184	$104.18	$104.20	$104.20
Purchase #5	$93.97	9.759%	$103.1405	$103.14	$103.15	$103.10
Purchase #6	$168.53	13.760%	$191.7197	$191.72	$191.70	$191.70
Purchase #7	$82.71	5.829%	$87.5312	$87.53	$87.55	$87.50
7 purchase totals =	$747.25		$809.6884	$809.68	$809.70	$809.70