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	$36.76	11.845%	$41.1142	$41.11	$41.10	$41.10
Purchase #2	$25.77	5.693%	$27.2371	$27.24	$27.25	$27.20
Purchase #3	$180.31	12.854%	$203.487	$203.49	$203.50	$203.50
Purchase #4	$142.96	9.729%	$156.8686	$156.87	$156.85	$156.90
Purchase #5	$99.39	9.672%	$109.003	$109.00	$109.00	$109.00
Purchase #6	$32.61	7.696%	$35.1197	$35.12	$35.10	$35.10
Purchase #7	$101.65	9.658%	$111.4674	$111.47	$111.45	$111.50
7 purchase totals =	$619.45		$684.2970	$684.30	$684.25	$684.30