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	$62.83	4.271%	$65.5135	$65.51	$65.50	$65.50
Purchase #2	$43.88	4.541%	$45.8726	$45.87	$45.85	$45.90
Purchase #3	$166.81	12.631%	$187.8798	$187.88	$187.90	$187.90
Purchase #4	$40.63	9.489%	$44.4854	$44.49	$44.50	$44.50
Purchase #5	$74.48	10.295%	$82.1477	$82.15	$82.15	$82.10
Purchase #6	$242.66	11.104%	$269.605	$269.61	$269.60	$269.60
Purchase #7	$76.33	12.666%	$85.998	$86.00	$86.00	$86.00
7 purchase totals =	$707.62		$781.5020	$781.51	$781.50	$781.50