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	$53.82	3.564%	$55.7381	$55.74	$55.75	$55.70
Purchase #2	$86.85	4.178%	$90.4786	$90.48	$90.50	$90.50
Purchase #3	$53.63	10.109%	$59.0515	$59.05	$59.05	$59.10
Purchase #4	$204.44	12.371%	$229.7313	$229.73	$229.75	$229.70
Purchase #5	$247.36	5.732%	$261.5387	$261.54	$261.55	$261.50
Purchase #6	$168.61	4.766%	$176.646	$176.65	$176.65	$176.60
Purchase #7	$28.83	8.180%	$31.1883	$31.19	$31.20	$31.20
7 purchase totals =	$843.54		$904.3725	$904.38	$904.45	$904.30