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	$10.46	13.338%	$11.8552	$11.86	$11.85	$11.90
Purchase #2	$26.28	7.253%	$28.1861	$28.19	$28.20	$28.20
Purchase #3	$191.54	9.286%	$209.3264	$209.33	$209.35	$209.30
Purchase #4	$98.89	10.709%	$109.4801	$109.48	$109.50	$109.50
Purchase #5	$132.34	6.654%	$141.1459	$141.15	$141.15	$141.10
Purchase #6	$108.34	10.265%	$119.4611	$119.46	$119.45	$119.50
Purchase #7	$163.81	3.205%	$169.0601	$169.06	$169.05	$169.10
7 purchase totals =	$731.66		$788.5149	$788.53	$788.55	$788.60