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	$76.44	3.336%	$78.99	$78.99	$79.00	$79.00
Purchase #2	$164.57	7.479%	$176.8782	$176.88	$176.90	$176.90
Purchase #3	$134.84	11.643%	$150.5394	$150.54	$150.55	$150.50
Purchase #4	$69.72	3.725%	$72.3171	$72.32	$72.30	$72.30
Purchase #5	$183.90	6.723%	$196.2636	$196.26	$196.25	$196.30
Purchase #6	$96.41	5.418%	$101.6335	$101.63	$101.65	$101.60
Purchase #7	$221.92	3.320%	$229.2877	$229.29	$229.30	$229.30
7 purchase totals =	$947.80		$1,005.9095	$1,005.91	$1,005.95	$1,005.90