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	$162.56	3.792%	$168.7243	$168.72	$168.70	$168.70
Purchase #2	$201.50	8.624%	$218.8774	$218.88	$218.90	$218.90
Purchase #3	$54.33	10.647%	$60.1145	$60.11	$60.10	$60.10
Purchase #4	$45.96	13.412%	$52.1242	$52.12	$52.10	$52.10
Purchase #5	$190.31	11.520%	$212.2337	$212.23	$212.25	$212.20
Purchase #6	$33.90	4.617%	$35.4652	$35.47	$35.45	$35.50
Purchase #7	$134.54	7.395%	$144.4892	$144.49	$144.50	$144.50
7 purchase totals =	$823.10		$892.0285	$892.02	$892.00	$892.00