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	$221.88	7.284%	$238.0417	$238.04	$238.05	$238.00
Purchase #2	$130.59	6.846%	$139.5302	$139.53	$139.55	$139.50
Purchase #3	$20.59	6.804%	$21.9909	$21.99	$22.00	$22.00
Purchase #4	$54.85	11.235%	$61.0124	$61.01	$61.00	$61.00
Purchase #5	$43.29	3.681%	$44.8835	$44.88	$44.90	$44.90
Purchase #6	$52.56	5.746%	$55.5801	$55.58	$55.60	$55.60
Purchase #7	$245.40	5.480%	$258.8479	$258.85	$258.85	$258.80
7 purchase totals =	$769.16		$819.8867	$819.88	$819.95	$819.80