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	$63.30	3.800%	$65.7054	$65.71	$65.70	$65.70
Purchase #2	$184.85	8.280%	$200.1556	$200.16	$200.15	$200.20
Purchase #3	$194.25	9.613%	$212.9233	$212.92	$212.90	$212.90
Purchase #4	$151.50	11.459%	$168.8604	$168.86	$168.85	$168.90
Purchase #5	$115.65	4.444%	$120.7895	$120.79	$120.80	$120.80
Purchase #6	$82.46	12.216%	$92.5333	$92.53	$92.55	$92.50
Purchase #7	$132.85	5.550%	$140.2232	$140.22	$140.20	$140.20
7 purchase totals =	$924.86		$1,001.1907	$1,001.19	$1,001.15	$1,001.20