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	$30.71	8.535%	$33.3311	$33.33	$33.35	$33.30
Purchase #2	$114.89	12.177%	$128.8802	$128.88	$128.90	$128.90
Purchase #3	$102.61	3.683%	$106.3891	$106.39	$106.40	$106.40
Purchase #4	$237.59	5.389%	$250.3937	$250.39	$250.40	$250.40
Purchase #5	$10.60	7.153%	$11.3582	$11.36	$11.35	$11.40
Purchase #6	$209.59	12.182%	$235.1223	$235.12	$235.10	$235.10
Purchase #7	$84.58	5.697%	$89.3985	$89.40	$89.40	$89.40
7 purchase totals =	$790.57		$854.8731	$854.87	$854.90	$854.90