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	$79.84	11.544%	$89.0567	$89.06	$89.05	$89.10
Purchase #2	$176.55	3.552%	$182.8211	$182.82	$182.80	$182.80
Purchase #3	$109.82	7.579%	$118.1433	$118.14	$118.15	$118.10
Purchase #4	$124.48	3.380%	$128.6874	$128.69	$128.70	$128.70
Purchase #5	$246.38	10.543%	$272.3558	$272.36	$272.35	$272.40
Purchase #6	$99.33	12.599%	$111.8446	$111.84	$111.85	$111.80
Purchase #7	$213.92	13.665%	$243.1522	$243.15	$243.15	$243.20
7 purchase totals =	$1,050.32		$1,146.0611	$1,146.06	$1,146.05	$1,146.10