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	$90.89	12.869%	$102.5866	$102.59	$102.60	$102.60
Purchase #2	$92.56	3.343%	$95.6543	$95.65	$95.65	$95.70
Purchase #3	$131.52	6.853%	$140.5331	$140.53	$140.55	$140.50
Purchase #4	$93.87	4.541%	$98.1326	$98.13	$98.15	$98.10
Purchase #5	$136.25	6.259%	$144.7779	$144.78	$144.80	$144.80
Purchase #6	$246.72	3.437%	$255.1998	$255.20	$255.20	$255.20
Purchase #7	$166.28	7.260%	$178.3519	$178.35	$178.35	$178.40
7 purchase totals =	$958.09		$1,015.2362	$1,015.23	$1,015.30	$1,015.30