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	$35.25	13.333%	$39.9499	$39.95	$39.95	$39.90
Purchase #2	$164.45	5.220%	$173.0343	$173.03	$173.05	$173.00
Purchase #3	$137.38	3.604%	$142.3312	$142.33	$142.35	$142.30
Purchase #4	$223.95	7.281%	$240.2558	$240.26	$240.25	$240.30
Purchase #5	$107.73	6.695%	$114.9425	$114.94	$114.95	$114.90
Purchase #6	$174.53	3.688%	$180.9667	$180.97	$180.95	$181.00
Purchase #7	$168.37	13.747%	$191.5158	$191.52	$191.50	$191.50
7 purchase totals =	$1,011.66		$1,082.9962	$1,083.00	$1,083.00	$1,082.90