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	$78.71	13.229%	$89.1225	$89.12	$89.10	$89.10
Purchase #2	$161.33	7.392%	$173.2555	$173.26	$173.25	$173.30
Purchase #3	$17.37	10.846%	$19.254	$19.25	$19.25	$19.30
Purchase #4	$68.35	7.849%	$73.7148	$73.71	$73.70	$73.70
Purchase #5	$160.81	11.860%	$179.8821	$179.88	$179.90	$179.90
Purchase #6	$241.43	6.376%	$256.8236	$256.82	$256.80	$256.80
Purchase #7	$112.95	11.346%	$125.7653	$125.77	$125.75	$125.80
7 purchase totals =	$840.95		$917.8178	$917.81	$917.75	$917.90