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	$155.25	11.294%	$172.7839	$172.78	$172.80	$172.80
Purchase #2	$92.46	5.298%	$97.3585	$97.36	$97.35	$97.40
Purchase #3	$137.78	10.235%	$151.8818	$151.88	$151.90	$151.90
Purchase #4	$203.85	4.301%	$212.6176	$212.62	$212.60	$212.60
Purchase #5	$129.65	13.635%	$147.3278	$147.33	$147.35	$147.30
Purchase #6	$115.70	10.640%	$128.0105	$128.01	$128.00	$128.00
Purchase #7	$168.65	3.874%	$175.1835	$175.18	$175.20	$175.20
7 purchase totals =	$1,003.34		$1,085.1636	$1,085.16	$1,085.20	$1,085.20