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	$223.42	6.737%	$238.4718	$238.47	$238.45	$238.50
Purchase #2	$89.37	8.301%	$96.7886	$96.79	$96.80	$96.80
Purchase #3	$26.67	13.540%	$30.2811	$30.28	$30.30	$30.30
Purchase #4	$129.67	9.349%	$141.7928	$141.79	$141.80	$141.80
Purchase #5	$127.46	12.580%	$143.4945	$143.49	$143.50	$143.50
Purchase #6	$84.39	7.616%	$90.8171	$90.82	$90.80	$90.80
Purchase #7	$27.52	3.870%	$28.585	$28.59	$28.60	$28.60
7 purchase totals =	$708.50		$770.2309	$770.23	$770.25	$770.30