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	$48.64	7.247%	$52.1649	$52.16	$52.15	$52.20
Purchase #2	$155.39	12.441%	$174.7221	$174.72	$174.70	$174.70
Purchase #3	$195.47	13.407%	$221.6767	$221.68	$221.70	$221.70
Purchase #4	$85.95	3.672%	$89.1061	$89.11	$89.10	$89.10
Purchase #5	$197.47	6.276%	$209.8632	$209.86	$209.85	$209.90
Purchase #6	$32.54	12.112%	$36.4812	$36.48	$36.50	$36.50
Purchase #7	$85.93	4.724%	$89.9893	$89.99	$90.00	$90.00
7 purchase totals =	$801.39		$874.0035	$874.00	$874.00	$874.10