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	$38.46	11.587%	$42.9164	$42.92	$42.90	$42.90
Purchase #2	$94.34	7.572%	$101.4834	$101.48	$101.50	$101.50
Purchase #3	$198.84	11.199%	$221.1081	$221.11	$221.10	$221.10
Purchase #4	$87.60	4.139%	$91.2258	$91.23	$91.25	$91.20
Purchase #5	$159.76	6.170%	$169.6172	$169.62	$169.60	$169.60
Purchase #6	$142.80	11.243%	$158.855	$158.86	$158.85	$158.90
Purchase #7	$138.75	5.357%	$146.1828	$146.18	$146.20	$146.20
7 purchase totals =	$860.55		$931.3887	$931.40	$931.40	$931.40