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	$94.96	5.185%	$99.8837	$99.88	$99.90	$99.90
Purchase #2	$215.71	9.813%	$236.8776	$236.88	$236.90	$236.90
Purchase #3	$179.73	12.348%	$201.9231	$201.92	$201.90	$201.90
Purchase #4	$85.45	9.558%	$93.6173	$93.62	$93.60	$93.60
Purchase #5	$103.92	7.667%	$111.8875	$111.89	$111.90	$111.90
Purchase #6	$214.56	9.338%	$234.5956	$234.60	$234.60	$234.60
Purchase #7	$136.83	11.466%	$152.5189	$152.52	$152.50	$152.50
7 purchase totals =	$1,031.16		$1,131.3037	$1,131.31	$1,131.30	$1,131.30