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	$28.48	12.815%	$32.1297	$32.13	$32.15	$32.10
Purchase #2	$42.44	5.662%	$44.843	$44.84	$44.85	$44.80
Purchase #3	$71.32	7.250%	$76.4907	$76.49	$76.50	$76.50
Purchase #4	$37.31	3.175%	$38.4946	$38.49	$38.50	$38.50
Purchase #5	$97.89	11.768%	$109.4097	$109.41	$109.40	$109.40
Purchase #6	$172.47	3.691%	$178.8359	$178.84	$178.85	$178.80
Purchase #7	$90.27	9.845%	$99.1571	$99.16	$99.15	$99.20
7 purchase totals =	$540.18		$579.3607	$579.36	$579.40	$579.30