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	$87.89	5.788%	$92.9771	$92.98	$93.00	$93.00
Purchase #2	$210.51	5.558%	$222.2101	$222.21	$222.20	$222.20
Purchase #3	$135.68	5.261%	$142.8181	$142.82	$142.80	$142.80
Purchase #4	$131.39	10.275%	$144.8903	$144.89	$144.90	$144.90
Purchase #5	$209.28	4.408%	$218.5051	$218.51	$218.50	$218.50
Purchase #6	$154.83	8.463%	$167.9333	$167.93	$167.95	$167.90
Purchase #7	$232.92	3.260%	$240.5132	$240.51	$240.50	$240.50
7 purchase totals =	$1,162.50		$1,229.8472	$1,229.85	$1,229.85	$1,229.80