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	$76.71	4.840%	$80.4228	$80.42	$80.40	$80.40
Purchase #2	$35.25	7.148%	$37.7697	$37.77	$37.75	$37.80
Purchase #3	$140.26	13.341%	$158.9721	$158.97	$158.95	$159.00
Purchase #4	$85.29	11.812%	$95.3645	$95.36	$95.35	$95.40
Purchase #5	$164.83	10.437%	$182.0333	$182.03	$182.05	$182.00
Purchase #6	$27.87	4.514%	$29.1281	$29.13	$29.15	$29.10
Purchase #7	$78.76	4.453%	$82.2672	$82.27	$82.25	$82.30
7 purchase totals =	$608.97		$665.9577	$665.95	$665.90	$666.00