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	$109.52	9.687%	$120.1292	$120.13	$120.15	$120.10
Purchase #2	$112.90	5.121%	$118.6816	$118.68	$118.70	$118.70
Purchase #3	$213.89	3.794%	$222.005	$222.01	$222.00	$222.00
Purchase #4	$93.69	7.123%	$100.3635	$100.36	$100.35	$100.40
Purchase #5	$161.87	11.251%	$180.082	$180.08	$180.10	$180.10
Purchase #6	$118.32	6.860%	$126.4368	$126.44	$126.45	$126.40
Purchase #7	$94.62	10.265%	$104.3327	$104.33	$104.35	$104.30
7 purchase totals =	$904.81		$972.0308	$972.03	$972.10	$972.00