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	$229.38	9.381%	$250.8981	$250.90	$250.90	$250.90
Purchase #2	$83.35	6.497%	$88.7652	$88.77	$88.75	$88.80
Purchase #3	$113.81	12.527%	$128.067	$128.07	$128.05	$128.10
Purchase #4	$47.70	12.239%	$53.538	$53.54	$53.55	$53.50
Purchase #5	$132.97	12.322%	$149.3546	$149.35	$149.35	$149.40
Purchase #6	$89.56	11.480%	$99.8415	$99.84	$99.85	$99.80
Purchase #7	$86.59	3.157%	$89.3236	$89.32	$89.30	$89.30
7 purchase totals =	$783.36		$859.7880	$859.79	$859.75	$859.80