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	$247.31	13.228%	$280.0242	$280.02	$280.00	$280.00
Purchase #2	$63.44	10.812%	$70.2991	$70.30	$70.30	$70.30
Purchase #3	$81.34	11.162%	$90.4192	$90.42	$90.40	$90.40
Purchase #4	$18.31	9.290%	$20.011	$20.01	$20.00	$20.00
Purchase #5	$147.31	6.122%	$156.3283	$156.33	$156.35	$156.30
Purchase #6	$128.44	3.340%	$132.7299	$132.73	$132.75	$132.70
Purchase #7	$61.69	10.308%	$68.049	$68.05	$68.05	$68.00
7 purchase totals =	$747.84		$817.8607	$817.86	$817.85	$817.70