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	$125.84	12.384%	$141.424	$141.42	$141.40	$141.40
Purchase #2	$177.64	8.112%	$192.0502	$192.05	$192.05	$192.10
Purchase #3	$10.26	4.191%	$10.69	$10.69	$10.70	$10.70
Purchase #4	$77.96	9.791%	$85.5931	$85.59	$85.60	$85.60
Purchase #5	$218.94	7.360%	$235.054	$235.05	$235.05	$235.10
Purchase #6	$83.87	8.433%	$90.9428	$90.94	$90.95	$90.90
Purchase #7	$105.40	5.455%	$111.1496	$111.15	$111.15	$111.10
7 purchase totals =	$799.91		$866.9037	$866.89	$866.90	$866.90