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	$231.66	11.220%	$257.6523	$257.65	$257.65	$257.70
Purchase #2	$77.34	10.105%	$85.1552	$85.16	$85.15	$85.20
Purchase #3	$39.82	12.324%	$44.7274	$44.73	$44.75	$44.70
Purchase #4	$136.85	12.409%	$153.8317	$153.83	$153.85	$153.80
Purchase #5	$87.71	4.334%	$91.5114	$91.51	$91.50	$91.50
Purchase #6	$94.25	9.625%	$103.3216	$103.32	$103.30	$103.30
Purchase #7	$63.32	13.588%	$71.9239	$71.92	$71.90	$71.90
7 purchase totals =	$730.95		$808.1235	$808.12	$808.10	$808.10