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	$71.82	12.175%	$80.5641	$80.56	$80.55	$80.60
Purchase #2	$219.69	5.346%	$231.4346	$231.43	$231.45	$231.40
Purchase #3	$36.83	13.507%	$41.8046	$41.80	$41.80	$41.80
Purchase #4	$73.74	11.594%	$82.2894	$82.29	$82.30	$82.30
Purchase #5	$64.70	13.311%	$73.3122	$73.31	$73.30	$73.30
Purchase #6	$167.37	5.629%	$176.7913	$176.79	$176.80	$176.80
Purchase #7	$151.38	3.448%	$156.5996	$156.60	$156.60	$156.60
7 purchase totals =	$785.53		$842.7958	$842.78	$842.80	$842.80