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	$50.40	6.154%	$53.5016	$53.50	$53.50	$53.50
Purchase #2	$94.26	4.299%	$98.3122	$98.31	$98.30	$98.30
Purchase #3	$228.82	11.258%	$254.5806	$254.58	$254.60	$254.60
Purchase #4	$250.99	5.787%	$265.5148	$265.51	$265.50	$265.50
Purchase #5	$98.57	5.382%	$103.875	$103.88	$103.90	$103.90
Purchase #6	$21.93	4.370%	$22.8883	$22.89	$22.90	$22.90
Purchase #7	$49.25	3.478%	$50.9629	$50.96	$50.95	$51.00
7 purchase totals =	$794.22		$849.6354	$849.63	$849.65	$849.70