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	$78.46	5.286%	$82.6074	$82.61	$82.60	$82.60
Purchase #2	$200.95	10.544%	$222.1382	$222.14	$222.15	$222.10
Purchase #3	$81.64	4.518%	$85.3285	$85.33	$85.35	$85.30
Purchase #4	$50.74	9.646%	$55.6344	$55.63	$55.65	$55.60
Purchase #5	$148.74	10.675%	$164.618	$164.62	$164.60	$164.60
Purchase #6	$107.56	11.662%	$120.1036	$120.10	$120.10	$120.10
Purchase #7	$160.40	13.144%	$181.483	$181.48	$181.50	$181.50
7 purchase totals =	$828.49		$911.9131	$911.91	$911.95	$911.80