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	$24.31	7.868%	$26.2227	$26.22	$26.20	$26.20
Purchase #2	$109.29	8.328%	$118.3917	$118.39	$118.40	$118.40
Purchase #3	$234.93	9.179%	$256.4942	$256.49	$256.50	$256.50
Purchase #4	$73.72	11.846%	$82.4529	$82.45	$82.45	$82.50
Purchase #5	$20.74	10.168%	$22.8488	$22.85	$22.85	$22.80
Purchase #6	$57.34	3.614%	$59.4123	$59.41	$59.40	$59.40
Purchase #7	$90.94	7.326%	$97.6023	$97.60	$97.60	$97.60
7 purchase totals =	$611.27		$663.4249	$663.41	$663.40	$663.40