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	$19.25	11.292%	$21.4237	$21.42	$21.40	$21.40
Purchase #2	$92.67	12.177%	$103.9544	$103.95	$103.95	$104.00
Purchase #3	$183.51	6.776%	$195.9446	$195.94	$195.95	$195.90
Purchase #4	$98.85	10.417%	$109.1472	$109.15	$109.15	$109.10
Purchase #5	$81.51	9.744%	$89.4523	$89.45	$89.45	$89.50
Purchase #6	$70.76	13.559%	$80.3543	$80.35	$80.35	$80.40
Purchase #7	$213.74	7.154%	$229.031	$229.03	$229.05	$229.00
7 purchase totals =	$760.29		$829.3075	$829.29	$829.30	$829.30