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	$52.81	6.665%	$56.3298	$56.33	$56.35	$56.30
Purchase #2	$208.99	13.814%	$237.8599	$237.86	$237.85	$237.90
Purchase #3	$168.63	10.142%	$185.7325	$185.73	$185.75	$185.70
Purchase #4	$114.88	13.641%	$130.5508	$130.55	$130.55	$130.60
Purchase #5	$56.79	4.700%	$59.4591	$59.46	$59.45	$59.50
Purchase #6	$109.29	9.286%	$119.4387	$119.44	$119.45	$119.40
Purchase #7	$19.60	7.688%	$21.1068	$21.11	$21.10	$21.10
7 purchase totals =	$730.99		$810.4776	$810.48	$810.50	$810.50