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	$45.69	12.283%	$51.3021	$51.30	$51.30	$51.30
Purchase #2	$83.59	8.476%	$90.6751	$90.68	$90.70	$90.70
Purchase #3	$189.50	13.545%	$215.1678	$215.17	$215.15	$215.20
Purchase #4	$163.77	10.847%	$181.5341	$181.53	$181.55	$181.50
Purchase #5	$180.29	8.128%	$194.944	$194.94	$194.95	$194.90
Purchase #6	$213.64	8.636%	$232.09	$232.09	$232.10	$232.10
Purchase #7	$85.93	3.749%	$89.1515	$89.15	$89.15	$89.20
7 purchase totals =	$962.41		$1,054.8646	$1,054.86	$1,054.90	$1,054.90