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	$26.32	5.116%	$27.6665	$27.67	$27.65	$27.70
Purchase #2	$170.31	5.761%	$180.1216	$180.12	$180.10	$180.10
Purchase #3	$96.95	12.576%	$109.1424	$109.14	$109.15	$109.10
Purchase #4	$64.34	3.243%	$66.4265	$66.43	$66.45	$66.40
Purchase #5	$200.53	6.166%	$212.8947	$212.89	$212.90	$212.90
Purchase #6	$28.67	9.761%	$31.4685	$31.47	$31.45	$31.50
Purchase #7	$46.86	7.588%	$50.4157	$50.42	$50.40	$50.40
7 purchase totals =	$633.98		$678.1359	$678.14	$678.10	$678.10