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	$25.95	5.459%	$27.3666	$27.37	$27.35	$27.40
Purchase #2	$150.69	7.433%	$161.8908	$161.89	$161.90	$161.90
Purchase #3	$56.46	12.156%	$63.3233	$63.32	$63.30	$63.30
Purchase #4	$250.62	5.425%	$264.2161	$264.22	$264.20	$264.20
Purchase #5	$158.63	8.520%	$172.1453	$172.15	$172.15	$172.10
Purchase #6	$54.86	12.871%	$61.921	$61.92	$61.90	$61.90
Purchase #7	$150.64	10.779%	$166.8775	$166.88	$166.90	$166.90
7 purchase totals =	$847.85		$917.7406	$917.75	$917.70	$917.70