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	$29.25	10.732%	$32.3891	$32.39	$32.40	$32.40
Purchase #2	$89.32	11.634%	$99.7115	$99.71	$99.70	$99.70
Purchase #3	$21.70	12.229%	$24.3537	$24.35	$24.35	$24.40
Purchase #4	$217.30	7.405%	$233.3911	$233.39	$233.40	$233.40
Purchase #5	$250.35	7.846%	$269.9925	$269.99	$270.00	$270.00
Purchase #6	$178.35	12.365%	$200.403	$200.40	$200.40	$200.40
Purchase #7	$223.60	3.807%	$232.1125	$232.11	$232.10	$232.10
7 purchase totals =	$1,009.87		$1,092.3534	$1,092.34	$1,092.35	$1,092.40