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	$77.94	5.750%	$82.4216	$82.42	$82.40	$82.40
Purchase #2	$71.97	9.177%	$78.5747	$78.57	$78.55	$78.60
Purchase #3	$59.96	8.124%	$64.8312	$64.83	$64.85	$64.80
Purchase #4	$153.32	13.618%	$174.1991	$174.20	$174.20	$174.20
Purchase #5	$98.88	9.400%	$108.1747	$108.17	$108.15	$108.20
Purchase #6	$108.66	3.828%	$112.8195	$112.82	$112.80	$112.80
Purchase #7	$228.59	6.498%	$243.4438	$243.44	$243.45	$243.40
7 purchase totals =	$799.32		$864.4646	$864.45	$864.40	$864.40