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	$26.54	5.233%	$27.9288	$27.93	$27.95	$27.90
Purchase #2	$210.88	6.706%	$225.0216	$225.02	$225.00	$225.00
Purchase #3	$152.42	4.672%	$159.5411	$159.54	$159.55	$159.50
Purchase #4	$223.79	11.762%	$250.1122	$250.11	$250.10	$250.10
Purchase #5	$77.73	5.704%	$82.1637	$82.16	$82.15	$82.20
Purchase #6	$106.90	5.562%	$112.8458	$112.85	$112.85	$112.80
Purchase #7	$102.32	4.524%	$106.949	$106.95	$106.95	$106.90
7 purchase totals =	$900.58		$964.5622	$964.56	$964.55	$964.40