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	$28.53	8.792%	$31.0384	$31.04	$31.05	$31.00
Purchase #2	$23.68	11.855%	$26.4873	$26.49	$26.50	$26.50
Purchase #3	$26.34	11.456%	$29.3575	$29.36	$29.35	$29.40
Purchase #4	$19.29	3.152%	$19.898	$19.90	$19.90	$19.90
Purchase #5	$86.33	3.345%	$89.2177	$89.22	$89.20	$89.20
Purchase #6	$89.68	11.277%	$99.7932	$99.79	$99.80	$99.80
Purchase #7	$189.55	13.443%	$215.0312	$215.03	$215.05	$215.00
7 purchase totals =	$463.40		$510.8233	$510.83	$510.85	$510.80