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	$167.91	13.110%	$189.923	$189.92	$189.90	$189.90
Purchase #2	$134.75	7.390%	$144.708	$144.71	$144.70	$144.70
Purchase #3	$67.53	7.832%	$72.8189	$72.82	$72.80	$72.80
Purchase #4	$201.74	9.468%	$220.8407	$220.84	$220.85	$220.80
Purchase #5	$121.81	4.659%	$127.4851	$127.49	$127.50	$127.50
Purchase #6	$64.71	9.128%	$70.6167	$70.62	$70.60	$70.60
Purchase #7	$108.86	13.867%	$123.9556	$123.96	$123.95	$124.00
7 purchase totals =	$867.31		$950.3480	$950.36	$950.30	$950.30