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	$51.94	7.666%	$55.9217	$55.92	$55.90	$55.90
Purchase #2	$53.62	7.543%	$57.6646	$57.66	$57.65	$57.70
Purchase #3	$64.51	11.291%	$71.7938	$71.79	$71.80	$71.80
Purchase #4	$22.32	9.665%	$24.4772	$24.48	$24.50	$24.50
Purchase #5	$138.30	11.117%	$153.6748	$153.67	$153.65	$153.70
Purchase #6	$224.57	12.804%	$253.3239	$253.32	$253.30	$253.30
Purchase #7	$167.47	3.222%	$172.8659	$172.87	$172.85	$172.90
7 purchase totals =	$722.73		$789.7219	$789.71	$789.65	$789.80