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	$129.37	11.729%	$144.5438	$144.54	$144.55	$144.50
Purchase #2	$6.61	9.615%	$7.2456	$7.25	$7.25	$7.20
Purchase #3	$34.25	8.597%	$37.1945	$37.19	$37.20	$37.20
Purchase #4	$82.89	8.457%	$89.9	$89.90	$89.90	$89.90
Purchase #5	$232.63	3.469%	$240.6999	$240.70	$240.70	$240.70
Purchase #6	$45.73	12.229%	$51.3223	$51.32	$51.30	$51.30
Purchase #7	$236.40	13.624%	$268.6071	$268.61	$268.60	$268.60
7 purchase totals =	$767.88		$839.5132	$839.51	$839.50	$839.40