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	$151.79	11.109%	$168.6524	$168.65	$168.65	$168.70
Purchase #2	$72.98	10.352%	$80.5349	$80.53	$80.55	$80.50
Purchase #3	$84.25	3.660%	$87.3336	$87.33	$87.35	$87.30
Purchase #4	$32.84	3.262%	$33.9112	$33.91	$33.90	$33.90
Purchase #5	$209.51	13.748%	$238.3134	$238.31	$238.30	$238.30
Purchase #6	$104.45	12.330%	$117.3287	$117.33	$117.35	$117.30
Purchase #7	$57.29	9.847%	$62.9313	$62.93	$62.95	$62.90
7 purchase totals =	$713.11		$789.0055	$788.99	$789.05	$788.90