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	$73.63	6.472%	$78.3953	$78.40	$78.40	$78.40
Purchase #2	$28.41	12.501%	$31.9615	$31.96	$31.95	$32.00
Purchase #3	$168.57	8.372%	$182.6827	$182.68	$182.70	$182.70
Purchase #4	$5.80	7.744%	$6.2492	$6.25	$6.25	$6.20
Purchase #5	$108.83	8.825%	$118.4342	$118.43	$118.45	$118.40
Purchase #6	$29.78	7.267%	$31.9441	$31.94	$31.95	$31.90
Purchase #7	$40.44	12.537%	$45.51	$45.51	$45.50	$45.50
7 purchase totals =	$455.46		$495.1770	$495.17	$495.20	$495.10