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	$72.90	10.577%	$80.6106	$80.61	$80.60	$80.60
Purchase #2	$112.69	5.539%	$118.9319	$118.93	$118.95	$118.90
Purchase #3	$173.81	12.499%	$195.5345	$195.53	$195.55	$195.50
Purchase #4	$104.85	10.784%	$116.157	$116.16	$116.15	$116.20
Purchase #5	$184.86	12.824%	$208.5664	$208.57	$208.55	$208.60
Purchase #6	$98.87	10.488%	$109.2395	$109.24	$109.25	$109.20
Purchase #7	$71.79	7.671%	$77.297	$77.30	$77.30	$77.30
7 purchase totals =	$819.77		$906.3369	$906.34	$906.35	$906.30