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	$28.71	10.485%	$31.7202	$31.72	$31.70	$31.70
Purchase #2	$80.47	5.529%	$84.9192	$84.92	$84.90	$84.90
Purchase #3	$180.88	8.851%	$196.8897	$196.89	$196.90	$196.90
Purchase #4	$43.95	6.159%	$46.6569	$46.66	$46.65	$46.70
Purchase #5	$141.54	3.524%	$146.5279	$146.53	$146.55	$146.50
Purchase #6	$68.33	13.822%	$77.7746	$77.77	$77.75	$77.80
Purchase #7	$104.82	7.233%	$112.4016	$112.40	$112.40	$112.40
7 purchase totals =	$648.70		$696.8901	$696.89	$696.85	$696.90