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	$26.47	12.706%	$29.8333	$29.83	$29.85	$29.80
Purchase #2	$103.56	8.561%	$112.4258	$112.43	$112.45	$112.40
Purchase #3	$31.96	3.348%	$33.03	$33.03	$33.05	$33.00
Purchase #4	$94.89	7.496%	$102.003	$102.00	$102.00	$102.00
Purchase #5	$80.47	4.143%	$83.8039	$83.80	$83.80	$83.80
Purchase #6	$18.71	8.193%	$20.2429	$20.24	$20.25	$20.20
Purchase #7	$25.36	13.243%	$28.7184	$28.72	$28.70	$28.70
7 purchase totals =	$381.42		$410.0573	$410.05	$410.10	$409.90