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	$32.89	12.161%	$36.8898	$36.89	$36.90	$36.90
Purchase #2	$21.73	9.803%	$23.8602	$23.86	$23.85	$23.90
Purchase #3	$104.95	12.640%	$118.2157	$118.22	$118.20	$118.20
Purchase #4	$85.85	4.316%	$89.5553	$89.56	$89.55	$89.60
Purchase #5	$133.72	7.603%	$143.8867	$143.89	$143.90	$143.90
Purchase #6	$60.69	4.296%	$63.2972	$63.30	$63.30	$63.30
Purchase #7	$109.65	7.223%	$117.57	$117.57	$117.55	$117.60
7 purchase totals =	$549.48		$593.2749	$593.29	$593.25	$593.40