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	$84.43	5.487%	$89.0627	$89.06	$89.05	$89.10
Purchase #2	$208.84	9.667%	$229.0286	$229.03	$229.05	$229.00
Purchase #3	$16.60	6.220%	$17.6325	$17.63	$17.65	$17.60
Purchase #4	$53.59	11.841%	$59.9356	$59.94	$59.95	$59.90
Purchase #5	$124.87	8.871%	$135.9472	$135.95	$135.95	$135.90
Purchase #6	$171.98	11.447%	$191.6666	$191.67	$191.65	$191.70
Purchase #7	$85.59	4.571%	$89.5023	$89.50	$89.50	$89.50
7 purchase totals =	$745.90		$812.7755	$812.78	$812.80	$812.70