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	$128.78	11.155%	$143.1454	$143.15	$143.15	$143.10
Purchase #2	$102.56	8.612%	$111.3925	$111.39	$111.40	$111.40
Purchase #3	$37.56	13.782%	$42.7365	$42.74	$42.75	$42.70
Purchase #4	$153.32	10.547%	$169.4907	$169.49	$169.50	$169.50
Purchase #5	$141.40	4.150%	$147.2681	$147.27	$147.25	$147.30
Purchase #6	$180.88	7.752%	$194.9018	$194.90	$194.90	$194.90
Purchase #7	$154.96	8.673%	$168.3997	$168.40	$168.40	$168.40
7 purchase totals =	$899.46		$977.3347	$977.34	$977.35	$977.30