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	$124.71	10.473%	$137.7709	$137.77	$137.75	$137.80
Purchase #2	$35.39	3.461%	$36.6148	$36.61	$36.60	$36.60
Purchase #3	$121.88	11.654%	$136.0839	$136.08	$136.10	$136.10
Purchase #4	$202.28	9.830%	$222.1641	$222.16	$222.15	$222.20
Purchase #5	$126.71	10.703%	$140.2718	$140.27	$140.25	$140.30
Purchase #6	$146.64	6.417%	$156.0499	$156.05	$156.05	$156.00
Purchase #7	$37.34	12.180%	$41.888	$41.89	$41.90	$41.90
7 purchase totals =	$794.95		$870.8434	$870.83	$870.80	$870.90