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	$85.32	5.225%	$89.778	$89.78	$89.80	$89.80
Purchase #2	$72.28	9.353%	$79.0403	$79.04	$79.05	$79.00
Purchase #3	$27.72	5.478%	$29.2385	$29.24	$29.25	$29.20
Purchase #4	$12.52	6.745%	$13.3645	$13.36	$13.35	$13.40
Purchase #5	$78.59	12.412%	$88.3446	$88.34	$88.35	$88.30
Purchase #6	$7.46	5.348%	$7.859	$7.86	$7.85	$7.90
Purchase #7	$54.47	12.506%	$61.282	$61.28	$61.30	$61.30
7 purchase totals =	$338.36		$368.9069	$368.90	$368.95	$368.90