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	$27.64	13.771%	$31.4463	$31.45	$31.45	$31.40
Purchase #2	$53.86	9.603%	$59.0322	$59.03	$59.05	$59.00
Purchase #3	$70.76	8.645%	$76.8772	$76.88	$76.90	$76.90
Purchase #4	$225.71	6.116%	$239.5144	$239.51	$239.50	$239.50
Purchase #5	$93.25	4.437%	$97.3875	$97.39	$97.40	$97.40
Purchase #6	$94.72	11.618%	$105.7246	$105.72	$105.70	$105.70
Purchase #7	$124.91	4.712%	$130.7958	$130.80	$130.80	$130.80
7 purchase totals =	$690.85		$740.7780	$740.78	$740.80	$740.70