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	$100.40	12.833%	$113.2843	$113.28	$113.30	$113.30
Purchase #2	$127.66	12.332%	$143.403	$143.40	$143.40	$143.40
Purchase #3	$82.34	3.800%	$85.4689	$85.47	$85.45	$85.50
Purchase #4	$144.92	9.805%	$159.1294	$159.13	$159.15	$159.10
Purchase #5	$52.79	4.391%	$55.108	$55.11	$55.10	$55.10
Purchase #6	$133.76	7.314%	$143.5432	$143.54	$143.55	$143.50
Purchase #7	$63.71	3.490%	$65.9335	$65.93	$65.95	$65.90
7 purchase totals =	$705.58		$765.8703	$765.86	$765.90	$765.80