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	$222.59	8.336%	$241.1451	$241.15	$241.15	$241.10
Purchase #2	$194.52	5.236%	$204.7051	$204.71	$204.70	$204.70
Purchase #3	$8.50	6.464%	$9.0494	$9.05	$9.05	$9.00
Purchase #4	$222.60	9.474%	$243.6891	$243.69	$243.70	$243.70
Purchase #5	$64.41	5.210%	$67.7658	$67.77	$67.75	$67.80
Purchase #6	$55.56	7.859%	$59.9265	$59.93	$59.95	$59.90
Purchase #7	$82.82	7.501%	$89.0323	$89.03	$89.05	$89.00
7 purchase totals =	$851.00		$915.3133	$915.33	$915.35	$915.20