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	$51.82	5.608%	$54.7261	$54.73	$54.75	$54.70
Purchase #2	$133.93	9.362%	$146.4685	$146.47	$146.45	$146.50
Purchase #3	$87.47	10.625%	$96.7637	$96.76	$96.75	$96.80
Purchase #4	$168.73	6.830%	$180.2543	$180.25	$180.25	$180.30
Purchase #5	$20.53	6.241%	$21.8113	$21.81	$21.80	$21.80
Purchase #6	$143.48	6.545%	$152.8708	$152.87	$152.85	$152.90
Purchase #7	$234.34	4.502%	$244.89	$244.89	$244.90	$244.90
7 purchase totals =	$840.30		$897.7847	$897.78	$897.75	$897.90