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	$41.57	7.181%	$44.5551	$44.56	$44.55	$44.60
Purchase #2	$10.73	3.541%	$11.1099	$11.11	$11.10	$11.10
Purchase #3	$104.75	13.273%	$118.6535	$118.65	$118.65	$118.70
Purchase #4	$204.43	9.315%	$223.4727	$223.47	$223.45	$223.50
Purchase #5	$168.34	10.421%	$185.8827	$185.88	$185.90	$185.90
Purchase #6	$214.30	3.594%	$222.0019	$222.00	$222.00	$222.00
Purchase #7	$75.46	13.259%	$85.4652	$85.47	$85.45	$85.50
7 purchase totals =	$819.58		$891.1410	$891.14	$891.10	$891.30