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	$32.84	9.154%	$35.8462	$35.85	$35.85	$35.80
Purchase #2	$18.88	11.352%	$21.0233	$21.02	$21.00	$21.00
Purchase #3	$208.73	4.507%	$218.1375	$218.14	$218.15	$218.10
Purchase #4	$97.82	6.184%	$103.8692	$103.87	$103.85	$103.90
Purchase #5	$179.32	6.193%	$190.4253	$190.43	$190.45	$190.40
Purchase #6	$156.27	11.828%	$174.7536	$174.75	$174.75	$174.80
Purchase #7	$105.51	6.294%	$112.1508	$112.15	$112.15	$112.20
7 purchase totals =	$799.37		$856.2059	$856.21	$856.20	$856.20