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	$163.83	3.475%	$169.5231	$169.52	$169.50	$169.50
Purchase #2	$221.56	8.402%	$240.1755	$240.18	$240.20	$240.20
Purchase #3	$37.95	11.671%	$42.3791	$42.38	$42.40	$42.40
Purchase #4	$145.78	12.871%	$164.5433	$164.54	$164.55	$164.50
Purchase #5	$108.93	5.307%	$114.7109	$114.71	$114.70	$114.70
Purchase #6	$93.51	6.658%	$99.7359	$99.74	$99.75	$99.70
Purchase #7	$198.35	5.228%	$208.7197	$208.72	$208.70	$208.70
7 purchase totals =	$969.91		$1,039.7875	$1,039.79	$1,039.80	$1,039.70