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	$201.37	10.463%	$222.4393	$222.44	$222.45	$222.40
Purchase #2	$174.87	11.465%	$194.9188	$194.92	$194.90	$194.90
Purchase #3	$192.72	11.838%	$215.5342	$215.53	$215.55	$215.50
Purchase #4	$24.82	13.423%	$28.1516	$28.15	$28.15	$28.20
Purchase #5	$82.44	10.448%	$91.0533	$91.05	$91.05	$91.10
Purchase #6	$83.62	8.623%	$90.8306	$90.83	$90.85	$90.80
Purchase #7	$96.87	3.206%	$99.9757	$99.98	$100.00	$100.00
7 purchase totals =	$856.71		$942.9035	$942.90	$942.95	$942.90