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	$122.30	13.251%	$138.506	$138.51	$138.50	$138.50
Purchase #2	$203.88	12.230%	$228.8145	$228.81	$228.80	$228.80
Purchase #3	$231.89	9.578%	$254.1004	$254.10	$254.10	$254.10
Purchase #4	$164.73	3.181%	$169.9701	$169.97	$169.95	$170.00
Purchase #5	$176.77	11.360%	$196.8511	$196.85	$196.85	$196.90
Purchase #6	$150.41	3.133%	$155.1223	$155.12	$155.10	$155.10
Purchase #7	$164.32	9.507%	$179.9419	$179.94	$179.95	$179.90
7 purchase totals =	$1,214.30		$1,323.3063	$1,323.30	$1,323.25	$1,323.30