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	$78.68	3.287%	$81.2662	$81.27	$81.25	$81.30
Purchase #2	$160.50	13.760%	$182.5848	$182.58	$182.60	$182.60
Purchase #3	$89.54	12.338%	$100.5874	$100.59	$100.60	$100.60
Purchase #4	$128.78	5.698%	$136.1179	$136.12	$136.10	$136.10
Purchase #5	$167.49	8.410%	$181.5759	$181.58	$181.60	$181.60
Purchase #6	$212.52	4.623%	$222.3448	$222.34	$222.35	$222.30
Purchase #7	$188.35	12.752%	$212.3684	$212.37	$212.35	$212.40
7 purchase totals =	$1,025.86		$1,116.8454	$1,116.85	$1,116.85	$1,116.90