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	$80.59	11.747%	$90.0569	$90.06	$90.05	$90.10
Purchase #2	$80.48	10.112%	$88.6181	$88.62	$88.60	$88.60
Purchase #3	$167.96	3.500%	$173.8386	$173.84	$173.85	$173.80
Purchase #4	$181.47	5.859%	$192.1023	$192.10	$192.10	$192.10
Purchase #5	$49.47	6.145%	$52.5099	$52.51	$52.50	$52.50
Purchase #6	$65.82	7.766%	$70.9316	$70.93	$70.95	$70.90
Purchase #7	$32.70	3.527%	$33.8533	$33.85	$33.85	$33.90
7 purchase totals =	$658.49		$701.9107	$701.91	$701.90	$701.90